Question: why is 4096 the max value for vlans

Answer: Only 12 bits are used for VLANs in 802.1q


Question: what is the difference between null and zero?

Answer: NULL is not a value, its a lack of one. Zero is still a value

Answer: 0 is the number 0. NULL is nirvana, nothing, nada, niente, non-existence, absence

Answer: 0 is about measurable quantity, while NULL is about existence

Answer: 0 is a numeric value where NULL is not


Question: how do i equally balance tmux(1) split panes?

Answer: use ctrl-b space to cycle through layouts with even spacing

Answer: From the command line you can use tmux select-layout tiled to make your splits all roughly equal size


Question: what are chains in iptables?

Answer: lists of rules, processed in order


Question: what is /storage/emulated/0/?

Answer: /storage/emulated/0/ is actually /data/media/0/ exposed through an emulated / virtual filesystem


Question: how to check what apps are running in android 6.0?

Answer: This is now in the Developer options area of your device settings, under the "Running Services" menu

Answer: go to Settings, Memory, "Memory used by apps


Question: how do i get sublime texts open-file gui to show hidden files?

Answer: press ⌘ cmd + ⇧ shift + . while the dialog is open


Question: can i change the behavior of the home and end keys on an apple keyboard with numeric keypad?

Answer: enable the "Use PC Style Home/End" setting in Karabiner


Question: how can i add new folders to the favorites in the finder sidebar?

Answer: Drag the folder to the desired position in the sidebar


Question: at what point does something count as security through obscurity?

Answer: where you rely upon some fact which you hope is not known to an attacker


Question: what is a bind mount?

Answer: an alternate view of a directory tree

Answer: A bind mount instead takes an existing directory tree and replicates it under a different point


Question: what is the difference between bash_profile and profile?

Answer: bash_profile work under bash, but ~/.profile work under Bourne and Korn shell


Question: how do i find out what hard disks are in the system?

Answer: lshw -class disk

Answer: fdisk -l command


Question: can a cvv code be 000?

Answer: 000 is perfectly valid


Question: what does the clock symbol mean on facebook messenger?

Answer: means that you haven't sent the message yet


Question: torvalds quote about good programmer

Answer: the overall high-level design (data-structures and their relationships) is much more important than the implementation details

Answer: I care that you can understand the things that will solve the problems I'm dealing with


Question: how to use terminal to copy a file to the clipboard?

Answer: Open a terminal and run: cat ~/Desktop/ded.html | pbcopy The file is now in your clipboard


Question: how to open files via terminal

Answer: type open followed by the filename/path


Question: how should i set up emergency access to business-critical secrets in case i am hit by a bus?

Answer: create separate accounts for key systems that have full access, but are not intended for everyday use


Question: how to get full path of original file of a soft symbolic link?

Answer: realpath


Question: how to add repository from shell in debian?

Answer: append the repository to /etc/apt/sources.list


Question: can tls work without certificates?

Answer: TLS itself could do encryption without certificates

Answer: You can have SSL/TLS without certificates


Question: macos sierra doesn’t seem to remember ssh keys between reboots

Answer: solution is calling ssh-add -A command on every startup

Answer: Amending ~/.ssh/config to add UseKeyChain for all hosts is enough to stop this recurring nightmare


Question: why is rhel not free?

Answer: it charges for doing the work in building from the SRPMs, and providing enterprise-grade support


Question: how to avoid being asked passphrase each time i push to bitbucket

Answer: use an ssh agent

Answer: Create (or edit if it exists) the following ~/.ssh/config file: Host * UseKeychain yes AddKeysToAgent yes IdentityFile ~/.ssh/id_rsa


Question: how do you exit full screen mode in yosemite?

Answer: Click the minimize/maximize button a second time or press Control-Command-F simultaneously

Answer: put the cursor in the upper left hand corner and wait a second


Question: how to delete directories based on `find` output?

Answer: Assume you are using gnu find, you can use the -delete option: find . -name test -delete


Question: how to convert a heif/heic image to jpeg in el capitan?

Answer: use the command line tool imagemagick to convert HEIC images to JPG


Question: how do i determine the number of ram slots in use?

Answer: sudo dmidecode -t memory | grep -i size


Question: how to move all files and folders via mv command

Answer: mv /path/sourcefolder/* /path/destinationfolder/

Answer: in Bash (I think this depends on your shell quite a bit...) $ mv source/{,.}* /destination/folder/here

Answer: cd /SourceDir && find ./ -maxdepth 1 -mindepth 1 -exec mv -t /Target/Dir {} + P. S

Answer: zsh: mv /src/*(D) /dst/ (D) to include dot-files


Question: how to monitor cpu/memory usage of a single process?

Answer: top -p $(pidof <process_name>)


Question: how to install desktop environments on centos 7?

Answer: $ sudo yum groupinstall "GNOME Desktop" $ ln -sf /lib/systemd/system/runlevel5.target /etc/systemd/system/default.target


Question: how to connect 2 monitors to macbook pro 2018?

Answer: use USB-C to DisplayPort cables


Question: refresh changed content of file opened in vi(m)

Answer: use the :edit command, without specifying a file name

Answer: :edit!

Answer: :e

Answer: :edit


Question: where do magic hashing constants like 0x9e3779b9 and 0x9e3779b1 come from?

Answer: 0x9e3779b9 is the integral part of the Golden Ratio's fractional part


Question: what are the differences between the security onion and kali distributions?

Answer: Kali is primarily an offensive security distribution for Penetration Testing and research and Security Onion is a defensive distribution for Network Security Monitoring


Question: do alarms play through headphones?

Answer: No,


Question: trying to sort on two fields, second then first

Answer: sort -k2,2 -k1


Question: ctrl + alt + delete: mac equivalent?

Answer: command + option + escape


Question: is there some ssh server for android?

Answer: Yes, there are a couple of options for this, including: SSHDroid

Answer: QuickSSHD

Answer: Dropbear


Question: is your ssh password revealed when you attempt to connect to the wrong server?

Answer: the remote server gets the password in plaintext

Answer: When using password authentication, you are transmitting your password to that server


Question: where are books stored after ibooks migration on mavericks?

Answer: They are now buried inside the user Library folder. The full path is: ~/Library/Containers/com.apple.BKAgentService/Data/Documents/iBooks/Books


Question: can git be used locally?

Answer: possible to use git locally

Answer: Yes


Question: tool to quickly hide/blur/redact text in screenshot?

Answer: Skitch can do this quickly

Answer: facepixelizer.


Question: why are chips safer than magnetic stripes?

Answer: can't clone the chip

Answer: an attacker cannot easily copy the card

Answer: a vendor can't simply copy it when you use it


Question: where should a local executable be placed?


Question: how to uppercase the command line argument?

Answer: echo "lowercase" | tr a-z A-Z Output: LOWERCASE


Question: clone ownership and permissions from another file?

Answer: stat: chmod $( stat -f '%p' ${reference} ) ${files}

Answer: Linux or Cygwin, you can use chmod --reference and chown —reference

Answer: Code: chmod $( stat -f '%p' "$1" ) "${@:2}" Usage: cp-permissions <from> <to>...

Answer: cp -p --attributes-only


Question: how does systemd use /etc/init.d scripts?

Answer: compatibility with van Smoorenburg rc scripts is achieved with a conversion program, named systemd-sysv-generator

Answer: systemd-sysv-generator generates the service units that run the van Smoorenburg rc scripts from /etc/init.d


Question: how big should my time machine backup drive be?

Answer: Time Machine needs 2 to 4 times as much space as the data it's backing-up

Answer: If you are really only using 120Gb, then potentially an external drive of 240-360Gb could well be enough


Question: how does the sticky bit work?

Answer: it prevents unprivileged users from removing or renaming a file in the directory unless they own


Question: has many vs belongs to?

Answer: One table (the "belongs to"-side) contains a foreign key to the other table (the "has many"-side


Question: how to transfer files from mac with broken screen?

Answer: connect it via Thunderbolt or Firewire to another Mac

Answer: remove the drive from the Mac and use a cheap $5 USB to SATA connector


Question: can ipv6 connect to ipv4?

Answer: cannot directly communicate


Question: how can i test if a variable is empty or contains only spaces?

Answer: try this: [[ $var = *[$" \t\n"]* ]]

Answer: Or with xargs: [[ -z $(echo $var | xargs) ]]


Question: are ssh usernames case sensitive?

Answer: definitely case sensitive

Answer: Unix usernames are definitely case-sensitive


Question: what is the proper term for ipaddress/hostname:port

Answer: Socket Address Pair

Answer: endpoint

Answer: authority


Question: can you still facetime if your number is blocked?

Answer: No

Answer: NO


Question: how can i list all user accounts in the terminal?

Answer: I used it to find lost hidden account. dscl . list /Users | grep -v '^_'

Answer: dscl . list /Users | grep -v "^_"


Question: how vlans communicate with each other?

Answer: through a layer-3 device


Question: how can i get a count of files in a directory using the command line?

Answer: using ls/wc pair is ls -Aq | wc -l


Question: what is this symbol? ⎋ (it is listed as menu shortcut)

Answer: is the Apple way of saying 'The ESC Key

Answer: the ⎋ is the Escape key located on the upper left side of your keyboard

Answer: That icon ⎋ is the Escape key

Answer: It is the escape key (esc)


Question: how can i verify the authenticity of an apk file i downloaded?

Answer: try to verify the public key contained within the .apk


Question: write to ntfs-formated drives on yosemite

Answer: use Paragon NTFS


Question: homebrew: rollback from python 3.7 to python 3.6.5.x?

Answer: install Python 3.6.5_1 from previous formula this way:

Answer: brew switch python 3.x.x_x # Ex. 3.6.5_1


Question: what does ` (backquote/backtick) mean in commands?

Answer: whatever inside it is interpreted as the result of that command

Answer: runs the contents of the enclosed string

Answer: Everything you type between backticks is evaluated (executed) by the shell before the main command


Question: is the oft-cited xkcd scheme [...] no longer good advice?

Answer: The XKCD password scheme is as good as it ever was


Question: where does lineageos store update files?

Answer: the updates are stored in /data/lineageos_updates


Question: how can i achieve page-up and page-down in os x?

Answer: ⌥ + Up/Down arrow keys

Answer: fn + shift + ↑/↓


Question: is there a one-liner that allows me to create a directory and move into it at the same time?

Answer: mkdir longtitleproject && cd $_


Question: how do you check if a port is blocked on linux?

Answer: use netstat -tuplen | grep 25

Answer: use iptables -nL | grep to see if there is any rule set by your firewall


Question: what is the difference between process and job?

Answer: A process is any running program with its own address space. A job is a concept used by the shell


Question: in a bash script, using the conditional or in an if statement

Answer: if [ "$fname" = "a.txt" -o "$fname" = "c.txt" ]


Question: make all new files in a directory accessible to a group

Answer: control the assigned permission bits with umask, and the group by making the directory setgid to GROUPNAME

Answer: change the directory's ACL to give the group write permissions and to make these permissions inherited


Question: how can i see who is connected to my hotspot?

Answer: Unfortunately no GUI exists in iOS for finding details about connected devices to the wireless hotspot

Answer: Setting>Tap on the name of your Hot spot and you'll see the names

Answer: With a network scanner app like Net Analyzer running on your iPhone


Question: where are certs stored on iphone?

Answer: in Settings → General → About → Certificate Trust Settings


Question: why is number of open files limited in linux?

Answer: the operating system needs memory to manage each open file, and memory is a limited resource


Question: time machine backup how much space?

Answer: 2 to 4 times as much space as the data it's backing-up


Question: does the shebang determine the shell which runs the script?

Answer: Yes


Question: when using the single responsibility principle, what constitutes a responsibility?

Answer: A "responsibility" is catering to a single business function


Question: what is 1 &2 in unix?

Answer: 1 - stdout 2 - stderr

Answer: It's swapping stdout and stderr


Question: how can i display the contents of a text file on the command line?

Answer: command to display content of a text file. cat filename

Answer: cat filename

Answer: Use cat command

Answer: One option is to use more e.g. more file.txt


Question: are there keyboard shortcuts for home, end, pagedown, and pageup in os x?

Answer: the fn and the arrow keys: fn+↑ is PageUp fn+↓ is PageDown fn+← is Home fn+→ is End


Question: what is oversubscription in networking?

Answer: refers to potentially requiring more resources from a device, link, or component than are actually available

Answer: concept of providing more downstream capacity than your infrastructure can actually provide


Question: pdf cannot be opened because it is from an unidentified developer?

Answer: solution is simply to do xattr -d com.apple.quarantine


Question: how can i prevent an ssh session from hanging in os x terminal?

Answer: Configure your system, system-wide, for all connections By editing: /etc/ssh/ssh_config And add the line: ServerAliveInterval 10

Answer: Add these two lines to /etc/ssh/ssh_config: ServerAliveInterval 60 TCPKeepAlive yes

Answer: Automatically reconnect ssh after sleep or wifi interruption Install autossh from MacPorts or Homebrew


Question: why do we need a 3-way handshake? why not just 2-way?

Answer: both parties need to synchronize their segment sequence numbers used during their transmission

Answer: a two way handshake would only allow one party to establish an ISN


Question: finding all large files in the root filesystem

Answer: find / -xdev -type f -size +100M It lists all files that has size bigger than 100M


Question: if you ^z from a process, it gets stopped. how do you switch back in?

Answer: bring it to the foreground


Question: how to transfer files from iphone to pc without wifi?

Answer: The charging cable serves both as a charging cable and a data transfer cable


Question: how to remove a single line from history?

Answer: history -d linenumber


Question: xfce how to switch workspace?

Answer: default shortcuts. These are Ctrl+Alt+1, Ctrl+Alt+2, and so on


Question: how do quick & dirty programmers know they got it right?

Answer: They don't


Question: is android showing app ads in share menu now?

Answer: Microsoft is abusing Android’s share sheet by inserting ads for its apps with reddit and Android Police links


Question: how to run a command without hitting enter key?

Answer: CTRL+O


Question: what is the difference between programming and computer science?

Answer: CS is about the theoretical capabilities of computers, where programming is about the practical application

Answer: Computer science is the study of what computers [can] do; programming is the practice of making computers do


Question: compress a folder with tar?

Answer: tar czf name_of_archive_file.tar.gz name_of_directory_to_tar


Question: what is the difference between error and fault?

Answer: A fault is the adjudged or hypothesized cause of an error


Question: what is the difference between delete from library and remove download?

Answer: Remove Downloads will leave the playlist in your library, but remove the music files associated with the songs


Question: how can usb sticks be dangerous?

Answer: can be used to trick the operating system into executing code


Question: can ipv6 talk to ipv4?

Answer: cannot directly communicate


Question: need a cli to check the sha256 hash of a file

Answer: use openssl dgst -sha256 Tested on LibreSSL 2.6.4 on macOS 10.14 (Mojave

Answer: you can use openssl sha -sha256 or openssl sha256

Answer: shasum -a 256 -c <<<'_paste hash to compare here_ *_path to file goes here_'


Question: how to prevent mac from changing the order of desktops/spaces

Answer: System Prefs > Mission Control Uncheck Automatically rearrange Spaces based on most recent use


Question: why are people making tables with divs?

Answer: table elements have rendering limitations that don't exist for div elements

Answer: because the css allows for much more flexible rendering


Question: where is the folder that termux defaults to?

Answer: The default directory is: /data/data/com.termux/files/home

Answer: on the CLI, type $ pwd and data/data/com.termux/files/home should appear


Question: how to show hidden files and folders in finder?

Answer: defaults write com.apple.finder AppleShowAllFiles true killall Finder To switch back, do the same but substitute false for true

Answer: In the Finder, press CommandShift. to show hidden files & folders


Question: what are the security reasons for disallowing the plus sign in email addresses?

Answer: There is no valid security reason

Answer: there are no real security reasons


Question: how do i run a .sh or .command file in terminal

Answer: Open Terminal, type in sh /path/to/file and press enter

Answer: type sh and a space and then drag the file to the window


Question: how to search for android apps without ads?

Answer: you could use Yalp or a fork of Yalp, Aurora (F-droid link), it has many search filters


Question: does bcrypt have a maximum password length?

Answer: Yes, BCrypt has an upper limit of 72 characters

Answer: 72 bytes


Question: certificate has been revoked reason superseded?

Answer: the certificate has been superseded but there is no cause to suspect that the private key has been compromised


Question: are time machine backups password protected?

Answer: Not by default


Question: how umount device is busy?

Answer: I was logged in more than once


Question: is it safe to send clear usernames/passwords on a https connection to authenticate users?

Answer: As long as you verify the certificate validity, this is perfectly fine


Question: how can i capture traffic on cisco ios switches?

Answer: use the Embedded Packet Capture feature


Question: how to retrieve the wi-fi password of a connected network on a mac

Answer: Spotlight → Keychain Access → type Wi-Fi name → select key → enter password to see Wi-Fi password


Question: tdd who writes the tests?

Answer: by the developer

Answer: the person writing the component


Question: how do i transfer files from my mac with a broken screen?

Answer: connect it via Thunderbolt or Firewire to another Mac

Answer: remove the drive from the Mac and use a cheap $5 USB to SATA connector


Question: how can i find available network interfaces?

Answer: ifconfig -a

Answer: cat /proc/net/dev


Question: how to recursively find the amount stored in directory?

Answer: use "file-size.sh" from the awk Velour library: ls -ARgo "$@" | awk '{q += $3} END {print q}'


Question: is the save button delay in a firefox download dialog a security feature? what does it protect?

Answer: the delay is to prevent attacks based around tricking the user into entering input to skip past the dialog


Question: move folder content up one level

Answer: cp -vaR foo/. . && rmdir foo/


Question: how can i shutdown my android phone using an adb command?

Answer: adb shell reboot -p to shutdown the phone


Question: how can i mount sftp/ssh in finder on os x snow leopard?

Answer: use Homebrew and Cask to install osxfuse and sshfs


Question: do ibooks backup to icloud?

Answer: eBook content are backed up to iCloud

Answer: Yes


Question: what tool exists to identify the rgb value of a pixel?

Answer: use DigitalColor Meter (in Utilities)

Answer: Use the built-in app /Applications/Utilities/DigitalColor Mete

Answer: use SpotColor (recently renamed to Hues, more info here) and HexPicker

Answer: use macOS' built-in Digital Color Meter


Question: why does my phone charge so slow on usb?

Answer: because the voltage and amperage provided by the computer is considerably lower


Question: most efficient method to empty the contents of a file

Answer: truncate -s 0 filename

Answer: cp /dev/null filename


Question: how to copy a file from a remote server to a local machine?

Answer: scp username@source:/location/to/file username@destination:/where/to/put

Answer: rsync -avzh --stats --progress remoteuser@remoteip:/path/ localpath

Answer: scp -r root@178.62.54.83:~/folderinremoteuserdir ~/folderinlocaluserdir


Question: what is the actual size of an ethernet mtu

Answer: 1500 bytes


Question: support for multiple users on same device

Answer: Titanium Backup has very limited support for this

Answer: SwitchMe app just appeared featuring profiles for root users. The free version is able to manage 2 profiles

Answer: With the update to 4.1.2, multiple user profiles can be configured

Answer: This is available for phones starting in Android 5.0


Question: how do i set an environment variable on the command line and have it appear in commands?

Answer: TEST=foo && echo $TEST


Question: how to terminate a background process?

Answer: use the command pkill to kill the job by name

Answer: type jobs then use the job number to kill it

Answer: use kill $!

Answer: use -9 flag on kill command


Question: why jsp is used instead of servlet?

Answer: easier to code and to read when you are creating a dynamic HTML front-end


Question: can iphone x case be used for xs?

Answer: X case will fit onto the XS but that the camera lens does not align properly


Question: what is the offical name of the third on-screen button?

Answer: Task Switcher or Recent Tasks


Question: how can i type unicode characters without using the mouse?

Answer: first enable Unicode Hex Input in System Preferences -> Keyboard -> Input Sources


Question: is awk faster than grep?

Answer: grep will most likely be faster

Answer: in theory grep should be faster than awk


Question: how to change path in finder by entering the path manually?

Answer: Finder has a menu item found under Go ("Go to Folder…") where you can type a full path


Question: how to automatically login to captive portals on os x?

Answer: You can rename /System/Library/CoreServices/Captive Network Assistant.app into /System/Library/CoreServices/No More Captive Network Assistant.app

Answer: Tyilo's NetworkAutoLogin project on github is an os.x daemon that "Automagically logs into to Captive Portal Networks


Question: is it free to facetime?

Answer: You will be charged


Question: how can i save tabs in iterm 2 so they restore the next time the app is run?

Answer: Save and Restore Window Arrangement with ⇧ ⌘ S and ⇧ ⌘ R options under the Window screen

Answer: Open preferences General tab Startup Change to 'Use System window restoration setting'. Restart


Question: are vectors and arrays the same?

Answer: Vectors aren't exactly arrays

Answer: in the context of data structures, when they say vector they mean exactly array


Question: download using wget to a different directory than current directory

Answer: wget -P /var/cache/foobar/ [...] wget --directory-prefix=/var/cache/foobar/ [...]


Question: how can i find the implementations of linux kernel system calls?

Answer: A good place to read the Linux kernel source is the Linux cross-reference


Question: moving tmux pane to window

Answer: use bind-key j "join-pane -s !

Answer: By default, Ctrl+b, ! would break the active pane into a new window and switch to it


Question: consequences of deleting .ds_store

Answer: folder display attributes (icon positions and view settings) will go away

Answer: at worst custom Finder view settings (icon size, position, background color, etc) will be lost


Question: what is the difference between a key escrow and a recovery agent?

Answer: key escrow is someone who holds the keys for each user, while a recovery agent has a master key


Question: how to create nested directory in a single command?

Answer: mkdir -p x/y/z

Answer: the -p option

Answer: Your command should be: sudo mkdir -p x/y/z


Question: if my password was able to be printed on a form sent home from my childs school, does it imply insecure password storage policies?

Answer: they are clearly not following password storage best-practices


Question: what is the eval command in bash?

Answer: The eval statement tells the shell to take eval’s arguments as command and run them through the command-line


Question: did i just get dns hijacked?

Answer: your router's primary DNS entry was pointed to a rogue DNS server


Question: what is difference between $@ and $* in unix shell script?

Answer: $* is a single string, whereas $@ is an actual array


Question: is java slower than c++?

Answer: on average code written in Java will run slower than (roughly) equivalent code written in C++


Question: can you connect two airpods to one apple watch?

Answer: No


Question: how secure is blacking out sensitive information using ms paint?

Answer: When blacking out sensitive information in Paint the original pixels are destroyed


Question: is charging my iphone all night harmful?

Answer: No, it's not harmful

Answer: it won't hurt it in the short term, but in the long term it will shorten its lifespan


Question: how to change your date of birth on icloud?

Answer: no way to do this


Question: is there any particular reason to use diffie-hellman over rsa for key exchange?

Answer: DH ephemeral key exchange provides perfect forward secrecy, which RSA alone does not


Question: how to use pip after the os x el capitan upgrade?

Answer: install the modules only for the current user using pip install --user


Question: how to check who last logged in linux?

Answer: usually /var/log/wtmp and prints the entries of successful login attempts

Answer: use stat command: stat /var/log/wtmp


Question: how can i display the current dns servers from the command line under os x?

Answer: grep nameserver <(scutil --dns


Question: how do certification authorities store their private root keys?

Answer: the CA key will be stored in a Hardware Security Module

Answer: Thales HSM devices (6 figure £ costs) that had proper tamper proof systems for tilt, temperature, physical attack


Question: what is ^m line ending?

Answer: The ^M is a carriage-return character


Question: turning power chime off

Answer: create an empty AIFF file to replace the default chime


Question: how can i add a shortcut to a particular google drive document to my android homescreen?

Answer: press and hold on a blank area and click "Shortcuts". Select "Drive Shortcut", then your document

Answer: Open your app drawer and jump to the Widgets section. Swipe until you get to "Drive Shortcut

Answer: open the context menu on the document Scroll down if needed and click "add to homescreen


Question: copy text from one tmux pane to another (using vim)

Answer: use the system clip board with "*y and "*p

Answer: Enter copy mode: <prefix>+[ Start copy: <Space> Copy text: <Enter> Paste text: <prefix>+]


Question: how to keep screen turned off when plugging charger?

Answer: install Xposed, this module has an option to prevent the screen from waking


Question: what are whatsapp voice notes?

Answer: voice files that you recorded using your Whatsapp


Question: copy specific file type keeping the folder structure

Answer: find . -name '*.csv' -exec cp --parents \{\} /target \;

Answer: find -name "*.csv" | xargs cp --parents -t /target


Question: cmd+tab does not work on hidden or minimized windows

Answer: Uncheck "When switching to an application, switch to a Space with open windows for the application


Question: why igp is used in mpls?

Answer: provides connectivity for MP-BGP inside the network


Question: how to change notification sound whatsapp android?

Answer: select Notifications, which should be the bottom option on the list at the moment, and tap Notification Tone

Answer: Open the WhatsApp Chats Tab and use the three-dot-menu (top-right) and then > Settings > Notifications > Messages


Question: what is difference between class variable and instance variable?

Answer: Instance variables have separate values for each instance of a class. Class variables maintain a single shared value


Question: view stdout/stderr of systemd service

Answer: use the journalctl command


Question: why ospf has area 0?

Answer: to ensure that the SPF calculation is consistent and to prevent routing loops


Question: can uid and gid be the same?

Answer: by default the UID and the GID are equal for ordinary users


Question: how to move internal storage to sd card in samsung duos?

Answer: Settings→Apps→Manage Apps, sroll to the app you want to move, tapp the "Move to SDCard


Question: linux where are acls stored?

Answer: in the file inodes

Answer: Each shadow inode stores an ACL in its data blocks

Answer: typically stored in a separate data block on the disk


Question: how can i circumvent regional restrictions in googles play store?

Answer: using a VPN and a Google Play store e-mail address set to the region you want


Question: is there a tool to get the lines in one file that are not in another?

Answer: grep and comm (with sort


Question: how can i copy files from my mac to pc via microsoft remote desktop?

Answer: paste to \\tsclient\OSX\Users\Shared


Question: is apfs required for mojave?

Answer: No

Answer: YES


Question: what is the difference between echo and printf in unix?

Answer: echo adds a newline and printf doesn't


Question: how to list disks, partitions and filesystems in linux?

Answer: fdisk -l or parted -l, but probably the most handy is lsblk


Question: how to change your email name icloud?

Answer: click Accounts then change Full Name to how you'd like your name to appear


Question: why can i traceroute to this ip address, but not ping?

Answer: pings can be blocked (ICMP block) on a remote host but traceroute can still find the route

Answer: ping utility relies on the ICMP protocol which is sometimes blocked at the network firewall


Question: what is the difference between kali linux and debian?

Answer: Kali is based on Debian, but includes, some forked packages which aren't in Debian packages


Question: how do i clear the terminal history?

Answer: history -c

Answer: rm ~/.bash_history history -c

Answer: rm ~/.bash_history


Question: is mac os x unix?

Answer: yes

Answer: Yes


Question: how to define tab delimiter with cut in bash?

Answer: cut -f2 -d' ' infile or write it like this to use ANSI-C quoting: cut -f2 -d$'\t' infile


Question: what is the difference between iphone backup and sync?

Answer: Backup copies everything, but Sync only copies what you choose through iTunes


Question: how the f*&% to stop voice-to-text from censoring profanity?

Answer: There is a checkable/uncheckable option called Block offensive words under Settings → Voice input & output


Question: does dd copy empty space?

Answer: Yes it does


Question: how do i disable or get rid of the startup sound my mac makes?

Answer: use StartSound.PrefPane which basically just sets the volume to 0

Answer: download and install "StartupSound.prefPane

Answer: Hold down the mute button on your keyboard whenever you boot it


Question: how can i edit multiple files in vim?

Answer: use split windows - both horizontal and vertical - to edit multiple files


Question: how do i stop the adobe creative cloud app from auto-launching on login?

Answer: run launchctl unload -w /Library/LaunchAgents/com.adobe.AdobeCreativeCloud.plist

Answer: on the menu bar icon. Click the ellipsis icon at the top-right. Select “Preferences” Uncheck “Launch at login

Answer: Click the ellipsis icon at the top-right. Select “Preferences” Uncheck “Launch at login

Answer: disable its launchd jobs and the Adobe Core Sync extension


Question: how to colorize output of git?

Answer: use git config --global color.ui auto

Answer: git config --global color.ui auto git config --global color.branch auto git config --global color.status auto

Answer: For a colored git diff piped into less, this works: git -c color.diff=always diff [...] | less -R

Answer: add a color.diff section to ~/.gitconfig


Question: what is difference between find and ls?

Answer: ls only applies to the current working directory, while find applies to all files and subdirectories


Question: how to auto-hide the address bar in google chrome?

Answer: To get full screen w/o address bar in Chrome on OSX use Cmd-Shift-F

Answer: go to chrome://flags and then search for Immersive Fullscreen Toolbar and set the value to Enabled


Question: username and/or password invalid - why do websites show this kind of message instead of informing the user which one was wrong?

Answer: so that we are not as susceptible to brute-force or dictionary attacks

Answer: to prevent user enumeration attack


Question: how to move apps to sd card in samsung s duos?

Answer: Settings→Apps→Manage Apps, sroll to the app you want to move, tapp the "Move to SDCard


Question: why would i tar a single file?

Answer: to copy it preserving the timestamp


Question: is it ok to split long functions and methods into smaller ones even though they wont be called by anything else?

Answer: Yes


Question: do bright wallpapers spend more battery than dark ones?

Answer: On OLED, AMOLED and Super AMOLED screens: Yes LCD screens: No

Answer: I was saving 20% battery by switching to dark wallpaper and dark themed apps


Question: what is aead cipher suite?

Answer: AEAD stands for "Authenticated Encryption with Additional Data


Question: how to keep two versions of an app installed?

Answer: Change package name so that android will recognize it as a different app


Question: where can i find good dictionaries for dictionary attacks?


Question: what is a tainted kernel in linux?

Answer: non-GPL-compatible module or unsigned module


Question: how do you extract an apps data from a full backup made through adb backup?

Answer: with a one-liner: ( printf "\x1f\x8b\x08\x00\x00\x00\x00\x00" ; tail -c +25 backup.ab ) | tar xfvz -


Question: how can i delete a word backward at the command line (bash and zsh)?

Answer: Alt+Backspace works for me in bash and zsh

Answer: CtrlW


Question: are ssl certificates case sensitive?

Answer: No


Question: how can i show typing keyboard in record screen

Answer: try showing the on-screen keyboard


Question: where are apache file access logs stored?

Answer: /var/log and subdirectories


Question: is rsa a block cipher?

Answer: It is neither a stream cipher nor a block cipher

Answer: it's not


Question: is vlan 1 the native vlan?

Answer: yes

Answer: the Default Native VLAN is VLAN 1


Question: agile for the solo developer

Answer: Agile works just as well for individuals as it does for teams


Question: what is the page size in linux?

Answer: 4kB

Answer: 4kb


Question: why arp is layer 2 protocol?

Answer: broadcast is sent on layer 2 (data link layer) and ARP will normally not traverse to layer 3

Answer: defined as an ethertype inside an Ethernet-V2 frame, and it is not forwarded by standard IP routers


Question: mkdir when directory already exists?

Answer: mkdir WILL give you an error if the directory already exists


Question: is there a way to convert audio files in mac os x or the command line without using itunes?

Answer: use the CLI command afconvert


Question: how can i find out which users are in a group within linux?

Answer: groups

Answer: lid command

Answer: groupmems -g groupname -l


Question: extract only a specific file from a zipped archive to a given directory

Answer: unzip ARCHIVE_NAME PATH_OF_FILE_INSIDE_ARCHIVE


Question: where are contacts saved on android?

Answer: plain Vanilla Android" has them in /data/data/android.providers.contacts/databases


Question: how can paypal spoof emails so easily to say it comes from someone else?

Answer: anyone can fake any email address, including that "Sender" field


Question: how create a temporary file in shell script?

Answer: Use mktemp to create a temporary file temp_file=$(mktemp)


Question: how to tell gzip to keep original file?

Answer: use -k or —keep


Question: what versions of os x are affected by heartbleed?

Answer: no version of OS X is affected by Heartbleed

Answer: No versions of OS X are affected (nor is iOS affected


Question: can you put a kindle book on 2 devices?

Answer: up to six Kindles or Kindle-compatible devices


Question: how to disable auto suspend when i close laptop lid?

Answer: systemd-inhibit --what=handle-lid-switch sleep 1d


Question: how can i open a text file with textwrangler from the terminal (command line)?

Answer: If you have the TextWrangler command line tools installed you can use 'edit' to open files in TextWrangler

Answer: If you have the TextWrangler command line tools installed, you can just type edit my_text_file.txt in the terminal

Answer: /Applications/TextWrangler.app/Contents/MacOS/TextWrangler my_text_file.txt


Question: can you connect bluetooth headphones and regular headphones at the same time?

Answer: no


Question: what certificates are needed for multi-level subdomains?

Answer: wildcard cert


Question: where do i put my systemd unit file?


Question: does an iso27001 audit require users to reveal their passwords?

Answer: Absolutely not


Question: what is `^m` and how do i get rid of it?

Answer: to get rid of them, use this in Vim: :s/^M$// (Press Ctrl+V Ctrl+M to insert that ^M.)

Answer: open your file with vim -b FILE_PATH save it with following command :%s/^M//g


Question: ssl3 poodle vulnerability

Answer: an attack on the SSL 3.0 protocol.


Question: why would you not permit q or z in passwords?

Answer: Q and Z could signal a randomly generated password

Answer: On old phones, there were no letters "Q" or "Z

Answer: to have less work for the administrator in an environment with multiple keyboard layouts

Answer: rotary and touch-tone phones didn't have a Q or Z


Question: automated ssh-keygen without passphrase, how?

Answer: (example using default filename) cat /dev/zero | ssh-keygen -q -N ""

Answer: su - -c "echo |ssh-keygen -t rsa"

Answer: ssh-keygen -t rsa -f /home/oracle/.ssh/id_rsa -q -P ""

Answer: sudo -u username bash -c "ssh-keygen -f ~username/.ssh/id_rsa -N ''"


Question: how do i report a security vulnerability about a trusted certificate authority?

Answer: contact CERT: https://forms.cert.org/VulReport/


Question: what is the purpose of the hash command?

Answer: use it to remember executables in non-standard locations

Answer: Easy detection whether a command is available


Question: how can i tell if a green text message has been delivered?

Answer: iMessages have a build in delivery report and is will tell you tings like 'delivered


Question: how do i automate a key press in applescript?

Answer: Run a script like this in AppleScript Editor:


Question: how do i type ² or ³ on an apple keyboard (international english layout)?

Answer: (Command + Shift) + plus/equals key Then type number you want


Question: how to disable adobe core sync app on os x from being launched automatically?

Answer: disable the tool with launchctl directly or by using an Application like LaunchControl


Question: what does @ signify in unix file permissions?

Answer: If the file or directory has extended attributes, you'll see an @ in the permissions field

Answer: @ stands for extended attributes, in addition to the standard unix file permissions


Question: how do you hide your best friends on snapchat?

Answer: You cannot hide the best friends list in snapchat


Question: how to install pkg file on mac command line?

Answer: The installer command is used to install Mac OS X installer packages to a specified domain or volume

Answer: do sudo installer -verbose -pkg "$f" -target / done


Question: how are /dev linux files created?

Answer: mknod or automatically by udev


Question: how to merge all (text) files in a directory into one?

Answer: The command $ cat *


Question: how do i undo always show pictures from this sender on android gmail?

Answer: Now click the Menu button again to bring up sub-menu of options > Clear picture approvals

Answer: Gmail app > Settings > General Settings > Triple Dot Menu > Clear Picture Approvals


Question: what is the difference between the terms data structures and abstract data type?

Answer: an ADT (Abstract Data Type) is more of a logical description, while a Data Structure is concrete

Answer: ADT is to an interface (what it does) what a data structure is to a class


Question: sort based on the third column

Answer: sort -t : -k 3 filename


Question: uninstall apps locked by phone vendor

Answer: root your phone in order to remove preinstalled apps

Answer: You can't remove them without root

Answer: use ADB to remove applications


Question: bash - how to run a command after the previous finished?

Answer: have them on separate lines

Answer: join commands with ;


Question: magic mouse can never reconnect on yosemite

Answer: Turn off wifi Turn on wifi again Reconnect Magic Mouse


Question: how can i keep my ssh sessions from freezing?

Answer: screen on the remote host


Question: what is difference between man and help command?

Answer: help is a bash built-in, providing help for bash commands only man is the traditional form of help


Question: is password entry being recorded on camera a realistic concern?

Answer: yes, you describe a viable risk that the industry has been addressing for a long time.

Answer: recent example is when Kanye was caught on camera entering his "00000" password to unlock his device

Answer: yes, it is a very real-world concern


Question: how to set to open folder with enter in finder?

Answer: In Karabiner search menu (upper left): "use return as open

Answer: use BetterTouchTool to make the Enter key simulate ⌘ Command + ↓ Down Arrow key press


Question: how to force ssh client to use only password auth?

Answer: ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no example.com


Question: what is difference between function and features?

Answer: Function" is purpose and "Feature" is a product behavior that a user can interact with


Question: how do i download an ios app (ipa) file to my mac after itunes 12.7 update?

Answer: iMazing 2.5 for Mac and PC can download apps from the App Store and install .ipa files


Question: whats the meaning of a dot before a command in shell?

Answer: short hand for the bash built in source

Answer: same as the source command

Answer: . (source or dot operator) Read and execute commands from the filename argument in the current shell context


Question: how can i explain to non-techie friends that cryptography is good?

Answer: take their argument and replace "cryptography" with "locks and keys on our houses" and see if they still agree


Question: why zsh ends a line with a highlighted percent symbol?

Answer: to let you clearly see unterminated lines


Question: is zsh compatible with bash?

Answer: Zsh's syntax is not completely compatible with bash, but it's close


Question: how can i tell what version of linux im using?

Answer: uname command


Question: how do i kill all screens?

Answer: pkill screen Or killall screen

Answer: screen -wipe


Question: how to install dig on centos?

Answer: dnf install bind-utils

Answer: yum install bind-utils


Question: are there any tools to sandbox a malware application even more than the granted permissions on android?

Answer: XPrivacyLua is a module for Xposed framework which does exactly what you need


Question: is there an airdrop client for microsoft windows?

Answer: AirDrop for Win does not exist


Question: how to move and overwrite subdirectories (and files) to parent directory?

Answer: using the commands cp -r * .. followed by rm -rf *. I don't think you can "merge" directories using mv


Question: isnt ubuntus system prompt for my password spoofable?

Answer: there is no guarantee that the prompt comes from the operating system

Answer: Yes. This is insecure


Question: how can i set up a keyboard shortcut for switching input source?

Answer: Go to System Preferences → Keyboard → Shortcuts → Input Sources and define a keyboard shortcut


Question: how do i do a ls and then sort the results by date created?

Answer: to list files sorted by creation/birth date/time, you can use: ls -lt --time=birth

Answer: ls -l --time=birth


Question: can a file be executable but not readable?

Answer: users can run the script without being able to read it

Answer: You can setup a script so that it's not readable by the user, but still executable


Question: can home and end keys be mapped when using terminal?

Answer: Use control+a for HOME and control+e for END in Terminal

Answer: Terminal -> Preferences -> Profiles -> Keyboard and add: Key: ↖ Action: \033OH Key: ↗ Action: \033OF


Question: why we need igp in bgp?

Answer: because you don't want to carry your entire internet routing table in your IGP


Question: how do i limit the number of files printed by ls?

Answer: ls -U | head -4

Answer: ls -ld -- *([1,4]) to list the first 4 files


Question: do contacts get notified when you join whatsapp?

Answer: No


Question: how to know who connect to my iphone hotspot?

Answer: Setting>Tap on the name of your Hot spot and you'll see the names of the devices connected


Question: how do i set my dns when resolv.conf is being overwritten?

Answer: change the nameservers that dnsmasq uses by adding the following lines to /etc/dnsmasq.conf: server=8.8.8.8 server=8.8.4.4

Answer: # sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf


Question: how can i make press any key to continue

Answer: read -n 1 -s -r -p "Press any key to continue"


Question: does https prevent man in the middle attacks by proxy server?

Answer: No, the proxy cannot decrypt the data


Question: how can i make safari show the url when i hover over a link?

Answer: turn it on from View > Show Status Bar or with the ⌘/ shortcut


Question: how to update linux locate cache

Answer: sudo updatedb


Question: how do i hide the spotlight icon on yosemite, but keep the spotlight functionality?

Answer: Open System Preferences. Go to Dock & Menu Bar -> Spotlight. Uncheck Show in Menu Bar


Question: how does shutterstock keep getting my latest debit card number?

Answer: Shutterstock subscribes to Account Updater, and gets updated copies of your card info


Question: are online password generators safe?

Answer: It is not safe to generate passwords online


Question: change the python3 default version in ubuntu

Answer: change the simbolic link by ln -sf python3.6 python3 inside /usr/bin

Answer: update the symbolic link of python inside /usr/bin


Question: how can programming ability be used to help people in poverty?

Answer: Develop software which enables doctors/teachers to help/work with remote villages


Question: why are interfaces useful?

Answer: helps a system stay decoupled and thus easier to refactor, change, and redeploy


Question: what is the single most effective thing you did to improve your programming skills?

Answer: Read "Code complete" by Steve McConnell


Question: where on the file system are sms messages stored?

Answer: This is the absolute path to SMS and MMS DB on most android devices: /data/data/com.android.providers/telephony/databases/mmssms.db

Answer: the default path changed from: /data/data/com.android.providers/telephony/databases/mmssms.db to /data/data/com.android.providers.telephony/databases/mmssms.db

Answer: Looks like it moved to data/User_DE/0/com.android.providers.telephony/databases


Question: how to check if a port is blocked ubuntu?

Answer: use netstat -tuplen | grep 25

Answer: use iptables -nL | grep to see if there is any rule set by your firewall


Question: do symlinks take up space?

Answer: Symbolic links do take room


Question: what is the fedora equivalent of the debian build-essential package?

Answer: sudo dnf install make automake gcc gcc-c++ kernel-devel

Answer: For Fedora 23 and above: dnf install @development-tools


Question: where are sony xperia backups stored?

Answer: SD-Card/Android/data/SonyBnR/Backup

Answer: backups are located at /sdcard/.semc-fullbackup


Question: can i connect 2 bluetooth headphones to ipad?

Answer: no


Question: keyboard shortcut to unhide or unminimize a window in os x

Answer: When you ⌘ + ⇥ to that application, hold the ⌥ key before releasing ⌘

Answer: select any window with arrow keys, then press Option ⌥+Return ↩


Question: ssh-add complains: could not open a connection to your authentication agent

Answer: go to C:\$Installation_Folder$\Git\cmd and execute: start-ssh-agent


Question: what is the benefit of gits two-stage commit process (staging)?

Answer: the ability to commit a portion of a change


Question: what is the format of a .xip file

Answer: a xar derivative using gzip compression

Answer: contains an archive (xar containing a gzip archive and metadata) and a signature of the archive


Question: why does my dock keep moving back to my other monitor?

Answer: Apple didn't account for the over/under monitor configuration, the overhang catches your cursor and summons the dock


Question: how do i set environment variables on os x?

Answer: launchctl setenv environmentvariablename environmentvariablevalue


Question: is there a way to mute sound from one application on macos?

Answer: Audio Hijack Pro allows you to mute sound from any application

Answer: open source app, BackgroundMusic, that provides for per app volume control in OSX10.10+


Question: can you see when someone is looking at your location?

Answer: No


Question: what is the difference between two factor and two step verification?

Answer: two-step" is just a layperson-friendly name for two-factor authentication


Question: what is wrong with magic strings?

Answer: value is not checked at compile time


Question: is there a way to easily record a phone conversation in-progress?

Answer: download Voice Recorder from market. Turn on speakerphone during call with voice recorder running


Question: where can i find my crash logs?

Answer: Open the Console app from the Application -> Utilities, you will see the log files

Answer: you can see if it's in ~/Library/Logs or /Library/Logs

Answer: ~/Library/Logs/DiagnosticReports/ (where ~ refers to your Home directory


Question: where can find older versions of apps?

Answer: Some alternative repositories, such as F-Droid, allow you to choose which version you want to download

Answer: APKMirror from "Android Police

Answer: this site: apkpure


Question: how long does it take to restore icloud backup?

Answer: take 1-4 hours per gb


Question: what color codes can i use in my ps1 prompt?

Answer: Foreground colors 90 Dark gray 91 Light red 92 Light green 93 Light yellow 94 Light blue 95 Light magenta


Question: cat line x to line y on a huge file

Answer: X=57890000 Y=57890010 sed -n -e "$X,$Y p" -e "$Y q" filename

Answer: use tail -n "+$X" /path/to/file | head -n "$((Y-X+1))"


Question: how can i count the number of lines of a file with common tools?

Answer: your_command | wc -l

Answer: wc -l

Answer: wc -l myfile

Answer: awk 'END {print NR}' filename


Question: how to solve the issue that a terminal screen is messed up? (usually after a resizing)

Answer: Ctrl+L


Question: is it unusual for a small company (15 developers) not to use managed source/version control?

Answer: No definitely not


Question: disable line wrapping for output in the terminal

Answer: Pipe the output through less -S: -S or --chop-long-lines


Question: is 30 mbit/s fibre faster than 30 mbit/s copper?

Answer: 30 Mbit/s is the same speed, no matter if it runs over copper or fiber


Question: displaying combined file size of selected files in finder

Answer: Instead of ⌘+I use ⌘+⌥+I to see the info

Answer: Select the files right click hold alt (notice the menu options change) select 'Show Inspector


Question: zip the contents of a folder without including the folder itself

Answer: -j; for example: zip -r -j zipped_dir.zip folder/* It won’t zip 'root_folder

Answer: 7z a zipped.zip ./rootDir/*

Answer: 7z a zipped.zip ./rootDir/* ./rootDir/.[!.]*


Question: how do i delete all terminal mail?

Answer: go the direct route and just run : > /var/mail/$USER to empty the mail file


Question: reattach terminal tab to another window

Answer: hold down command + shift + option whilst dragging the body of the terminal

Answer: click and drag the tab from one window onto the tab bar of the other window


Question: what is yum equivalent of apt-get update?

Answer: yum makecache


Question: what is difference between ls and find?

Answer: ls only applies to the current working directory, while find applies to all files and subdirectories


Question: how can i keep my mac awake and locked?

Answer: use KeepingYouAwake

Answer: use free app Amphetamine. After app installation select the option Indefinitely.


Question: how to fix brew after osx upgrade to yosemite?

Answer: re-install brew


Question: can airpods connect to iphone and mac?

Answer: AirPods connect automatically with all your Apple devices

Answer: AirPods automatically switch between your iPhone, iPad, iPod touch, and Mac


Question: is there a specific reason for the poor readability of regular expression syntax design?

Answer: designed to be used as commands to a code editor, not as a language to code in


Question: what is tabnabbing?

Answer: a phishing technique where a malicious web site changes its looks while the tab is inactive


Question: why is bearer required before the token in authorization header in a http request?

Answer: Many web servers support multiple methods of authorization. In those cases sending just the token isn't sufficient

Answer: Bearer itself determines the type of authentication


Question: what do you do when code review is just too hard?

Answer: split up the changelist into multiple smaller changelists, which you then review one after another


Question: where are twrp file stored?

Answer: it should be at ./TWRP/BACKUPS/

Answer: root/data/media/0/TWRP/BACKUPS/

Answer: /data/media/0/TWRP/(backups folder


Question: how to move a window to another space without using the mouse?

Answer: Control + 1 Control + 2 Control + 3 etc

Answer: With Amethyst, you can send windows to specific spaces using configurable keyboard shortcuts


Question: rsync filter: copying one pattern only

Answer: rsync -avn --include="*.pdf" ~/Latex/ ~/Output/


Question: what happens if you plug more than one charger in the new macbook pro (2016)?

Answer: system will choose the power source that provides the most power


Question: failed to fetch jessie backports repository

Answer: use archive.debian.org instead


Question: why vlan range is 4096?

Answer: Only 12 bits are used for VLANs

Answer: 1 bit and VID(Vlan Identifier) =>12 bits. 2 power 12 is 4096


Question: why are z and y switched?

Answer: wrong language set for your keyboard


Question: what is the square icon on my iphone?

Answer: represents AirPlay


Question: are ipod classics still compatible with itunes?

Answer: iPod classic support is killed off in recent iTunes


Question: is hostgator storing my password in plaintext?

Answer: the Password is stored as an encrypted text

Answer: Yes, they store passwords in plaintext or equivalent


Question: why can i log in to my facebook account with a misspelled email/password?

Answer: the site tries to fix those misspellings automatically


Question: what is the difference between default gateway and router?

Answer: A gateway always has to be a router, but a router does not have to be a gateway


Question: how can i get the current working directory?

Answer: use the environment variable $PWD

Answer: write something like: dir=`pwd`

Answer: use: dir=$(/usr/bin/pwd)

Answer: dir=$(pwd -P)


Question: coding standard for clarity: comment every line of code?

Answer: No

Answer: the purpose of a comment is defeated if every line is commented


Question: cant use exclamation mark (!) in bash?

Answer: you need it enclosed in single quotes


Question: how to unzip a multipart (spanned) zip on linux?

Answer: 7z x archive.zip.001


Question: when choosing a numeric pin, does it help or hurt to make each digit unique?

Answer: ruling out repeated numbers increases security


Question: is there a quick way to relink my homebrew kegs?

Answer: brew list -1 | while read line; do brew unlink $line; brew link --force $line


Question: how do i write a retry logic in script to keep retrying to run it upto 5 times?

Answer: for i in 1 2 3 4 5; do command && break || sleep 15; done


Question: what is the formula for determining the number of possible hosts on a network?

Answer: 2**(32 - netmask_length


Question: homebrew: your clt does not support macos 11.0

Answer: fix this by downloading Command Line Tools for Xcode 12.3 from Apple website


Question: trying to ssh to local vm ubuntu with putty

Answer: VirtualBox: Right-click your virtual machine, select "Settings", and then select "Network". Next to "Attached to", select "Host-only Adapter


Question: is arp layer 2 or 3?

Answer: 2


Question: is there an imessage client for windows?

Answer: there currently exists no iMessage client for Windows

Answer: No, there is no iMessage client available for a Windows PC


Question: can i use gpl software in a commercial application

Answer: You can distribute your application using a GPL library commercially, but you must also provide the source code


Question: where are cwm backups stored?

Answer: stored in /sdcard/clockworkmod/backups//

Answer: ends being stored in /data/media/clockworkmod/backup


Question: click is not working trackpad?

Answer: do 1/4 turn left or right to adjust click on the trackpad


Question: how do i find out the applescript commands available for a particular app?

Answer: Alternately, you can drag an application icon to the Script Editor icon to display its dictionar


Question: how does imessage know that the recipient is an ios 5 device?

Answer: it uses the Device ID to determine if another device is running iOS 5


Question: in linux, how to delete all files except the pattern *.txt?

Answer: find . -type f ! -name '*.txt' -delete

Answer: (bash): shopt -s extglob rm !(*.txt)

Answer: $ find . -type f ! -name "*.txt" -exec rm -rf {} \;

Answer: rm $(ls -I "*.txt" )


Question: why was ~ chosen to represent the home directory?

Answer: practice derives from the Lear-Siegler ADM-3A terminal in common use during the 1970s


Question: what makes grep consider a file to be binary?

Answer: If there is a NUL character anywhere in the file


Question: macbook pro bluetooth audio balance keeps changing by itself

Answer: Enter Balance Lock - it will keep your audio centred and prevent left/right drift


Question: is a zip code considered pii?

Answer: Yes

Answer: Zip code is explicitly considered a HIPAA / Safe Harbor identifier


Question: how to remove an environment variable on osx using bash

Answer: unset DYLD_LIBRARY_PATH


Question: what is the difference between data structure and abstract data type?

Answer: an ADT (Abstract Data Type) is more of a logical description, while a Data Structure is concrete

Answer: ADT is to an interface (what it does) what a data structure is to a class


Question: virtualbox 5.1.28 fails to install on macos 10.13 due to kext security

Answer: reboot into safe mode, try the allow button there command line: sudo spctl --master-disable


Question: what is this folder /run/user/1000?

Answer: storing files used by running processes for that user


Question: make the green full screen window icon on yosemite maximize windows

Answer: Hold option and left click the green button to have it maximize

Answer: ⌘ + ⌥ + F


Question: xperia companion where are backups stored?

Answer: SD-Card/Android/data/SonyBnR/Backup

Answer: backups are located at /sdcard/.semc-fullbackup


Question: is xfce still being developed?

Answer: the project is still alive


Question: how to remove all empty directories in a subtree?

Answer: find . -depth -type d -exec rmdir {} +


Question: why does ipv6 specify 128 bit address, when there are only 48 bits in mac addresses?

Answer: to contain many MAC addresses you need to have the IP-space much bigger than the MAC address space


Question: can visa gift cards be traced?

Answer: Every transaction made with the card is tracked and reviewable


Question: if my team has low skill, should i lower the skill of my code?

Answer: not lower your programming skill, but you might need to adjust how you write code


Question: any reason not to run linux in a vm all the time?

Answer: OpenGL acceleration pass-through to the host is ropey

Answer: power consumption rises drastically whenever I start VirtualBox


Question: single application not showing up in spotlight

Answer: Go to System Preferences --> Spotlight --> Search Results Untick Applications Tick Applications


Question: how to list keys added to ssh-agent with ssh-add?

Answer: Use the -l option to ssh-add to list them by fingerprint


Question: how do i assign a keyboard shortcut to an applescript i wrote?

Answer: use a launcher that supports setting global hot keys and executing AppleScripts (Alfred, Keyboard Maestro, FastScripts


Question: why does vim indent pasted code incorrectly?

Answer: vim thinks you have typed the keys being pasted and does its own auto-indentation


Question: how to know whether wayland or x11 is being used

Answer: check whether WAYLAND_DISPLAY variable is set or not


Question: how to transfer files from pc to android emulator?

Answer: use adb push to copy files from Desktop to Emulator and adb pull for the reverse


Question: android phone charging slowly: how to make it faster

Answer: Plug to the wall rather than to a laptop. Try different USB cables


Question: how do i convert an epoch timestamp to a human readable format on the cli?

Answer: date -d @1190000000 Replace 1190000000 with your epoch

Answer: Custom format with GNU date: date -d @1234567890 +'%Y-%m-%d %H:%M:%S'

Answer: with GNU awk: awk 'BEGIN { print strftime("%Y-%m-%d %H:%M:%S", 1234567890); }'


Question: are in app purchases shared in family sharing?

Answer: they are not included

Answer: In App purchases are not shared in Family sharing


Question: when will my device get the android 4.0 update (ice cream sandwich)?

Answer: Phones Google Nexus ONE Official: never

Answer: HTC Amaze 4G Official: May-June (confirmed), June 16th 2012


Question: unable to modify the volume with the keyboard

Answer: Go to System Preferences -> Sound Adjust the slider bar at the bottom


Question: how to turn off all animations on os x

Answer: write -g NSAutomaticWindowAnimationsEnabled -bool false

Answer: write -g NSScrollAnimationEnabled -bool false


Question: what can i do when my ssh session is stuck?

Answer: Type ~. (i.e. tilde, period) at the beginning of a line

Answer: press Enter, then ~, then ..

Answer: ~. works


Question: command line: how do you rotate a pdf file 90 degrees?

Answer: For rotating clockwise: pdftk input.pdf cat 1-endeast output output.pdf

Answer: pdfjam --landscape --angle 90 input.pdf


Question: app does not appear on iphone?

Answer: Search with Spotlight, check for a new Home screen by swiping to the right, and check all


Question: where is desktop on linux?


Question: better colors so comments arent dark blue in vim?

Answer: do it manually with this command: :hi Comment guifg=#ABCDEF Where ABCDEF is an appropriate color hex code


Question: what is the purpose of using shift in shell scripts?

Answer: shift reassigns the positional parameters

Answer: shift treat command line arguments as a FIFO queue, it popleft element every time it's invoked


Question: how to extract specific file(s) from tar.gz

Answer: $ tar --extract --file=test.tar.gz subfolder/extract11

Answer: gunzip < thousands.tar.gz | tar -x -v --files-from hundreds.list -f -


Question: how to open multiple windows in outlook for mac?

Answer: go to File -> New -> Open New Main Window


Question: how can i add (subtract, etc.) two numbers with bash?

Answer: Arithmetic in POSIX shells is done with $ and double parentheses (( )): echo "$(($num1+$num2))

Answer: expr $num1 + $num2 In scripting $(()) is preferable since it avoids a fork/execute for the expr command


Question: can i change the application icon of an automator script?

Answer: Applications Folder Right-click on automator script Click on view package contents Add your icon to resources folder Rename

Answer: change the icon just as you would normally for any other folder


Question: how can i figure out whats slowly eating my hd space?

Answer: Download and run GrandPerspective

Answer: I suggest using applications (as suggested) like Grand Perspective or Disk Inventory X to find large files

Answer: Try the app disk cartography


Question: how can i make all folders in finder snap to grid?

Answer: Click on Show View Options In the "Sort by" drop down bar select "Snap to Grid


Question: is there any way to view saved wifi passwords on the iphone?

Answer: on the iPhone it is not possible to access this information

Answer: Jailbreak tweak WiFi Passwords from Cydia is the best one for viewing passwords directly on your iPhon


Question: how to change computer name so terminal displays it in mac os x mountain lion?

Answer: change it under System Preferences -> Sharing -> Computer Name


Question: how to transfer data from samsung duos to sd card?

Answer: Settings→Apps→Manage Apps, sroll to the app you want to move, tapp the "Move to SDCard


Question: the slash after an ip address - cidr notation

Answer: The slash following the IP address is the abbreviation for the subnet mask

Answer: a shorthand way to write a subnet mask

Answer: represents the bit length of the subnet mask

Answer: represents the subnet


Question: what is ge in unix?

Answer: greater-than or equal


Question: criticism and disadvantages of dependency injection

Answer: DI makes it much harder to navigate through code


Question: how do you detach the 2nd screen from within another screen?

Answer: ctrl-a a d


Question: how does linux handle multiple consecutive path separators (/home////username///file)?

Answer: Multiple slashes are allowed and are equivalent to a single slash

Answer: Multiple slashes get ignored (without effect)

Answer: it's the same as a single /


Question: how to see process created by specific user in unix/linux

Answer: use the following command: top -U [username]

Answer: ps -fp $(pgrep -u <username>)


Question: how to output only file names (with spaces) in ls -al?

Answer: ls -lA | awk '{print $9}'


Question: what is the rootless feature in el capitan, really?

Answer: What it really does is limit the power of the root account


Question: how to transfer edited photos from iphone to computer?

Answer: AirDrop or email the photo to yourself


Question: os x yosemite xcode update stuck on waiting

Answer: click on the "Store" in the top-left menu and choose the following option - "Check for Unfinished Downloads


Question: how to bring back multi-touch gestures after it crashes without reboot?

Answer: settings → trackpad, disable all scroll and zoom gestures, then reenable them

Answer: sudo killall hidd did work


Question: update bash to version 4.0 on osx

Answer: Install Bash 4 via Homebrew First install the newer version of bash


Question: how do i remove the google chrome notifications bell icon from the mac os x menu bar?

Answer: under "Chrome -> Hide Notification Icon" you can get rid of the bell


Question: zip all files in directory?

Answer: zip -r myfiles.zip mydir where mydir is the directory containing your files


Question: what does the broken pipe message mean in an ssh session?

Answer: your network (TCP) connection was reset


Question: what is nproc and nofile in linux?

Answer: nofile - max number of open file descriptors nproc - max number of processes


Question: how can i convince management to deal with technical debt?

Answer: construct a realistic case for a positive ROI on the work spent to pay down the technical debt

Answer: give your management a financial reason to deal with technical debt


Question: do you get notified when someone does find my iphone?

Answer: By default, no


Question: how can i send stdout to multiple commands?

Answer: commandoutput="$(command-to-run)" echo "$commandoutput" | grep -i errors echo "$commandoutput" | pbcopy

Answer: use tee and process substitution for this: cat file.txt | tee >(pbcopy) | grep errors

Answer: create multiple pipes and specify each of them as one output of tee


Question: move through images in a folder with preview.app

Answer: Open the directory & select all pictures using - "⌘ + A" Use - "⌘ + ↓


Question: find the total size of certain files within a directory branch

Answer: find ./photos/john_doe -type f -name '*.jpg' -exec du -ch {} + | grep total$

Answer: LC_ALL=C find ./photos/john_doe -type f -name '*.jpg' -exec du -ch {} + | grep total$

Answer: find -type f -iname *.jpg -print0 | du -ch --files0-from=- | grep total$


Question: are there naming conventions for variables in shell scripts?

Answer: use upper case and lower case (e.g. MY_CONSTANT and my_variable


Question: what is id in top?

Answer: id - Time spent in idle operations


Question: is anaconda safe to install?

Answer: yes, it is safe


Question: how to show all running launchctl daemons/agents?

Answer: To get all jobs loaded into launchctl use sudo launchctl list


Question: how do you turn off the try the new safari notification?

Answer: defaults write com.apple.coreservices.uiagent CSUIHasSafariBeenLaunched -bool YES

Answer: defaults write com.apple.coreservices.uiagent CSUIRecommendSafariNextNotificationDate -date 2050-01-01T00:00:00Z

Answer: defaults write com.apple.coreservices.uiagent CSUILastOSVersionWhereSafariRecommendationWasMade -float 10.99


Question: what does the .d stand for in directory names?

Answer: directory


Question: install shuf on os x?

Answer: install coreutils with brew install coreutils. shuf will be linked as gshuf

Answer: install coreutils with Macports


Question: installing .pkg with terminal ?

Answer: for f in *.pkg ; do sudo installer -verbose -pkg "$f" -target / done


Question: what are alternatives for menumeters on el capitan?

Answer: iStat Menus has a beta going for El Capitan right now

Answer: iStat Pro Widget 4.92


Question: should ssl be terminated at a load balancer?

Answer: SSL/TLS trust should terminate at the SSL offloading device


Question: whats the most appropriate directory where to place files shared between users?

Answer: /srv


Question: ios 12 is how many gb?

Answer: 5.1 GB

Answer: 7 GB


Question: how do i make `ls` show file sizes in megabytes?

Answer: ls -lh gives human readable file sizes, long format. It uses k, M, G, and T suffixes

Answer: --block-size=MB

Answer: ls -l —block-size=M

Answer: --block-size=1M


Question: convince apt-get *not* to use ipv6 method

Answer: Add -o Acquire::ForceIPv4=true when running apt-get


Question: elegant ways to handle if(if else) else

Answer: Extract it to separate function (method) and use return statement


Question: is ken thompsons compiler hack still a threat?

Answer: still a theoretical threat, but is not very likely


Question: are java pattern thread safe?

Answer: Java Pattern objects are thread safe


Question: why is video tearing such a problem in linux?

Answer: drivers that aren't there yet, and lack of vsync with certain window managers


Question: what is the difference between man and help in linux?

Answer: help is a bash built-in, providing help for bash commands only man is the traditional form of help


Question: is there any option with ls command that i see only the directories?

Answer: ls -ld -- */


Question: i dont have administrator account on my mac

Answer: Boot off the recovery partition, open up terminal, and type resetpassword

Answer: Boot into Recovery Partition, choose Terminal from the Utilities menu and type following: resetpassword


Question: if someone blocks you can they still facetime you?

Answer: No

Answer: NO


Question: what is the difference between an adt and a data structure?

Answer: an ADT (Abstract Data Type) is more of a logical description, while a Data Structure is concrete


Question: i deleted /bin/rm. how do i recover it?

Answer: obtaining the correct rm binary from another machine, and then using scp or something to copy it to the Pi


Question: should i contact the manufacturer if their product allows access to other users location information?

Answer: Yes, you should notify the problem to the company - with caution


Question: why doesnt mac os x source ~/.bashrc?

Answer: bash only reads .bashrc for non-login shells:

Answer: As Terminal starts bash as a login shell (run w to see that the bash instances are executed as -bash), .bashrc is never read automatically.


Question: how do i install gcc via homebrew?

Answer: can be installed using brew install

Answer: install GCC 4.8 by using brew tap homebrew/versions brew install [flags] gcc48

Answer: The best way to install GCC in homebrew right now is just brew install gcc


Question: hotkey to show hidden files and folders in file open dialog?

Answer: ⌘ CMD+⇧ SHIFT+

Answer: ⌘ CMD+⇧ SHIFT+G and type the path to the hidden folder, just like in Terminal


Question: whats the purpose of the randomart image for user (not host) ssh keys?

Answer: ease of validation

Answer: to differentiate between than long strings of hex code


Question: what is the website checking about my browser to protect the website from a ddos?

Answer: whether the HTTP client is a real browser or not


Question: whats the difference between $(stuff) and `stuff`?

Answer: you cannot nest backticks while you can nest $()


Question: how do i clear bashs cache of paths to executables?

Answer: $ hash -r Or just one entry: $ hash -d svnsync


Question: what is the difference between libreoffice and libreoffice vanilla?

Answer: LibreOffice Vanilla for Mac omits some Java-based features


Question: does thunderbolt 2 provide power?

Answer: yes


Question: execute a command once per line of piped input?

Answer: cat list.txt | xargs -I{} command parameter {} parameter


Question: is there any reason to disable paste password on login?

Answer: Disabling pasting a password field introduces a "Cobra effect


Question: how can i get distribution name and version number in a simple shell script?

Answer: use lsb_release -a

Answer: enter the following command: cat /etc/*-release


Question: why dhcp request is broadcast?

Answer: Because until the server sends the DHCPACK, the client still doesn’t have an IP address

Answer: to notify the other DHCP servers that have potentially sent offers that their offer isn't taken

Answer: By broadcasting the request message, all servers that may have issued an offer can be aware of the client's choice


Question: how can we run a command stored in a variable?

Answer: eval


Question: how to disable full screen animation on os x 10.9

Answer: Go to System Preferences > Accessibility > Display and check the box labeled Reduce motion


Question: can two uuid be same?

Answer: No


Question: how can i rename desktops / spaces in macos?

Answer: TotalSpaces by binaryage allows you to name Spaces


Question: can you add blank space to a photo in mac preview?

Answer: you can't do this in preview


Question: can crt contain private key?

Answer: file usually contains a single certificate, alone and without any wrapping (no private key


Question: how to apt-delete-repository?

Answer: Remove it from sources.list


Question: how do i disable system integrity protection (sip) aka rootless on macos [os x]

Answer: In the Terminal window, type in csrutil disable and press Enter

Answer: disable SIP by booting to Recovery HD and running the following command: csrutil disable


Question: how does google authenticator work?

Answer: Authenticator implements the Time-Based One-Time Password (TOTP) algorithm.


Question: how to access tmp folder on mac?

Answer: use browser (chrome, firefox), and in the URL bar :- file:///tmp/


Question: whats the recommended way of copying changes with vimdiff?

Answer: do (diff obtain) and dp (diff put)

Answer: use the normal commands :'<,'>diffget and :'<,'>diffput


Question: is bios written in assembly?

Answer: BIOS is written using Assembly


Question: what is the difference between inner join and join?

Answer: JOIN and INNER JOIN are the same


Question: should package names be singular or plural?

Answer: Use the plural for packages with homogeneous contents and the singular for packages with heterogeneous contents


Question: airmon ng is not recognized?

Answer: execute airmon-ng check kill before changing to monitor mode


Question: how do i change the name of my android device?

Answer: Application Settings > Development you will see the option 'Device hostname


Question: can i manually limit the %cpu used by a process?

Answer: There's CPUThrottle, which allows to specify a PID to restrict


Question: what vlan does cdp use?

Answer: CDP always chooses the lowest VLAN


Question: in centos, what is the difference between yum update and yum upgrade?

Answer: the difference is Upgrade will delete obsolete packages, while update will preserve them


Question: combined `mkdir` and `cd`?

Answer: eval {mkdir,cd}\ FOLDER\;


Question: what is the difference between directory and path?

Answer: Directory is where you are. Path is how to get there


Question: what is the minimum distance for single mode fiber?

Answer: 6.5 feet (2 m


Question: can i open files in textedit from the terminal in mac os x?

Answer: open -a TextEdit filename should do the trick


Question: how to clean log file?

Answer: > logfile or cat /dev/null > logfile


Question: why is it wrong to *implement* myself a known, published, widely believed to be secure crypto algorithm?

Answer: bugs can hide in crypto software without symptoms

Answer: easy to get cryptography wrong if you implement it yourself


Question: executing chdir before starting systemd service

Answer: [Service] WorkingDirectory=/usr/local


Question: are c strings null terminated?

Answer: C strings" will be null-terminated on any platform

Answer: C strings are null-terminated

Answer: null termination is pretty much universal for standard C


Question: what is gtkrc in linux?

Answer: gtkrc is the configuration file for Gtk, the GUI library used by GNOME applications and others


Question: why do we use ./ (dot slash) to execute a file in linux/unix?

Answer: to tell the shell where the executable is


Question: where are ppt templates stored on mac?

Answer: It is now ~/Library/Group Containers/UBF8T346G9.Office/User Content/Templates


Question: how do i find how long ago a linux system was installed?

Answer: rpm -qi basesystem


Question: ctrl-s hangs the terminal emulator?

Answer: C-s enables terminal scroll lock


Question: limit memory usage for a single linux process

Answer: /sys/fs/cgroup/memory/myGroup/memory.limit_in_bytes echo 5G > /sys/fs/cgroup/memory/myGroup/memory.memsw.limit_in_bytes


Question: prevent mac terminal from reverting to default theme

Answer: Terminal -> Preferences -> Settings -> Click desired Profile -> Click "Default" at the bottom of the frame

Answer: select which profile you want to be your default in the preferences for the Terminal application


Question: determine if git working directory is clean from a script

Answer: use empty output of git status —porcelain

Answer: Use: git diff-index --quiet HEAD The return code reflects the state of the working directory (0 = clean, 1 = dirty

Answer: Untracked files are ignored. if git diff-index --quiet HEAD then GIT_MODS="clean" else GIT_MODS="dirty" fi


Question: any way to encode the url in curl command?

Answer: curl -G "$( echo "$URL" | sed 's/ /%20/g' )"


Question: where does this concept of favor composition over inheritance come from?

Answer: GoF design patterns book


Question: do you need a wsdl for soap?

Answer: SOAP can be used without WSDL


Question: where can i find the task manager in mac os x lion?

Answer: Applications/Utilities/

Answer: use spotlight. Just type Activity monitor i.e mac task manager


Question: getting 256 colors to work in tmux

Answer: export TERM=xterm-256color or export TERM=screen-256color

Answer: export TERM=xterm-256color

Answer: set -g default-terminal "xterm-256color" set-option -ga terminal-overrides ",xterm-256color:Tc"


Question: is there a name for the (anti- ) pattern of passing parameters that will only be used several levels deep in the call chain?

Answer: The data itself is called "tramp data". It is a "code smell

Answer: tramp data


Question: how to see full log from systemctl status service?

Answer: journalctl -u service-name.service

Answer: systemctl -l status service-name

Answer: journalctl -xefu service-name.service or journalctl -xefu service-name


Question: find out current working directory of a running process?

Answer: readlink -e /proc/$$/cwd

Answer: pwdx $ pwdx <PID> lsof $ lsof -p <PID> | grep cwd /proc $ readlink -e /proc/<PID>/cwd

Answer: lsof -p PID | awk '$4=="cwd" {print $9}'


Question: what functionality do marks offer in the el capitan terminal?

Answer: allowing you to mark window positions


Question: how does gratuitous arp work?

Answer: it updates the ARP cache of other systems before they ask for it (no ARP request


Question: do any security experts recommend bcrypt for password storage?

Answer: Thomas Ptacek, the author and a security researcher recommends the usage of bcrypt


Question: where did the wheel group get its name?

Answer: derived from the slang term big wheel, referring to a person with great power or influence

Answer: from BSD


Question: what does <<< mean?

Answer: denotes a here string


Question: how do i grep recursively through .gz files?

Answer: find . -name \*.eml.gz -print0 | xargs -0 zgrep "STRING

Answer: zgrep -irs your-pattern-goes-here the-folder-to-search-goes-here/

Answer: use the find command to run zcat and grep against each file


Question: what is the difference between a function and a feature?

Answer: Function" is purpose and "Feature" is a product behavior


Question: do uninstalled apps take up space?

Answer: Uninstalled apps get their internal storage deleted automatically, but files they created can still take up space


Question: find command: how to ignore case?

Answer: -iname flag

Answer: find . -iname 'WSFY321.c


Question: how can i run ssh-add automatically, without a password prompt?

Answer: use ssh-keys that are not password protected


Question: disable automatic itunes launch when iphone is plugged in via usb

Answer: unselect either Open iTunes when this iPhone is connected, or Automatically sync when this iPhone is connected


Question: how does the authentication in the new uk £1 coin work?

Answer: it is chemical - ISIS is a plating system that uses a material that you can cheaply and accurately detect


Question: is post or get more secure?

Answer: POST is more secure than GET


Question: what does the clock symbol mean on messenger?

Answer: means that you haven't sent the message yet


Question: how do i transfer edited photos from my iphone to my computer?

Answer: AirDrop or email the photo to yourself


Question: is it possible to find out the hosts in the known_hosts file?

Answer: There is host string/ip at the beginning of each "known_hosts" line


Question: why is there a big delay after entering a wrong password?

Answer: to try and limit brute forcing


Question: what is java programmed in?

Answer: very first Java compiler developed by Sun Microsystems was written in C


Question: how to conditionally do something if a command succeeded or failed

Answer: if command ; then echo "Command succeeded" else echo "Command failed

Answer: use ||: rm -rf somedir || exit_on_error "Failed to remove the directory"

Answer: command && echo "OK" || echo "NOK"


Question: what is negative code?

Answer: reducing lines of code, by removing redundancies or using more concise constructs


Question: how can get a list of all scheduled cron jobs on my machine?

Answer: /var/spool/cron/* (user crontabs) /etc/crontab (system-wide crontab)


Question: what is wa in top?

Answer: wa - Time spent on waiting on IO peripherals (eg. disk


Question: is there any reason to use the var keyword in es6?

Answer: when you need a temp variable to be available within the scope of a block


Question: how can i open a .pkg file manually?

Answer: right click it, and click Show Package Contents you'll get a few files in a Contents folder

Answer: use the lsbom command

Answer: xar -xvf foo.pkg


Question: firmware-iwlwifi has no installation candidate?

Answer: Add "non-free" to your entries in /etc/apt/sources.list


Question: have backticks (i.e. `cmd`) in *sh shells been deprecated?

Answer: It's not deprecated


Question: xfce how to lock screen?

Answer: via command line $ xflock4


Question: how to choose directory name during untarring

Answer: mkdir pretty_name && tar xf ugly_name.tar -C pretty_name --strip-components 1

Answer: use --transform to apply a sed regexp transformation to each file name

Answer: tar zxvf ugly_name.tgz --one-top-level=pretty_name `--one-top-level[=dir

Answer: tar xvf dml/ugly_name.tar --one-top-level=pretty_name —strip-components 1


Question: do imessages show up on text logs?

Answer: it's not going to show up on the provider logs


Question: what is the difference between .bash_profile and .bashrc?

Answer: .bash_profile is executed for login shells, while .bashrc is executed for interactive non-login shells


Question: two html elements with same id attribute: how bad is it really?

Answer: never duplicate IDs within the same document


Question: how to distinguish nexus 7 (2012) and nexus 7 (2013)

Answer: The 2013 model also has a camera on the back, which the 2012 model lacks

Answer: The 2013 model has a notification LED on the front, which the 2012 model lacks


Question: what is /usr/local/bin?

Answer: default location for executable files


Question: how can i use gmail as the default mail client app in mac os x?

Answer: open settings, search for "mailto", and set Gmail as the handler for mailto


Question: how do i launch finder from terminal or command line

Answer: type open


Question: how to set path for finder-launched applications

Answer: sudo launchctl config user path


Question: disable command-w in the terminal

Answer: To disable ⌘W in Terminal, do the following

Answer: At the bottom of "Global Shortcut Keys" click "+", then type Cmd-W and leave the default Action "Ignore

Answer: iTerm2 → Preferences → keys → Add key mapping: "command + w" => ignore


Question: what is the purpose of gibberish comments posted to my blog?

Answer: They're probing your site

Answer: it's an attempt to check which of them will result in an actual HTML link

Answer: They are trying to confuse any automatic spam filters you might be using

Answer: lower the effectiveness of the filter


Question: can gid and uid be same?

Answer: by default the UID and the GID are equal for ordinary users


Question: how to transfer calendar from windows phone to android?

Answer: sync your WM phone with Google then when your Android mobile syncs


Question: what is ip forward-protocol nd?

Answer: means that the router will forward ND packets for diskless workstations