marco-a / TIL

TIL

20.02.2017 - Get PID from a port: lsof -n -i :PORT | grep LISTEN for example to get the process that is using port 80: lsof -n -i :80 | grep LISTEN.

01.03.2017 - tput is a useful command to interact with a TTY:  - tput cols get number of columns.  - tput lines get number of lines.  - tput sc save cursor position.  - tput rc restore cursor position.  - tput colors get number of supported colors.

01.03.2017 - When the dimensions of the terminal change a SIGWINCH signal is sent.

04.03.2017 - PHP's microtime and time do not return a monotonic timestamp. This is bad for timing because the returned timestamp is dependent on the user's time setting.

15.06.2017 - Use CTRL+Z to pause execution of a long command. To resume simply enter %.

23.07.2017 - When bundling packages it's common to set the owner and group to root:root. This is because when extracting as a normal user, tar will set the owner to the current user executing the command. However, extracting as root retains the owner and group from the tar archive. This can lead to wrong / corrupt ownership permissions. To set the root:root ownership without having to need root permissions you can use fakeroot to bundle the tar.

10.08.2017 - PHP's session_start() can return true even when the session was not created. Workaround: create a value and save it to disk to check if the disk storage is sufficient.

13.08.2017 - returning in a finally block causes an exception to be 'swallowed': A function can either throw an exception or return a value but not both.

19.11.2017 - Bash's command &> output is not POSIX compliant. Portable scripts should use command > output 2>&1.

06.03.2017 - Linux kernel modules:

• Load module: modprobe <module-name> <module-params>.
• Unload module: modprobe -r <module-name>.
• Force unload: rmmod -f <module-name>.
• List loaded modules: lsmod.

06.03.2017 - nandsim kernel module:

nandsim simulates a NAND chip:

first_id_byte=0x00 (manufacturer ID)

second_id_byte=0x00 (chip ID)

third_id_byte=0x00 (optional)

fourth_id_byte=0x00 (optional)

06.03.2017 - One can list all MT-devices with $ cat /proc/mtd.

06.03.2017 - Mounting an UBIFS image:

$ modprobe nandsim (first_id_byte ...)

$ modprobe ubi

$ ubiformat /dev/mtdX -y -f UBIFS.img (you may need to use -O and -s)

$ ubiattach -p /dev/mtdX

$ mount -t ubifs ubiX /path/to/mount/point/

Unmounting:

$ umount /path/to/mount/point/

$ ubidetach -p /dev/mtdX

09.03.2018 - Flickering animations in WebKit? Add transform: translate3d(0, 0, 0); to element before executing animation.

27.11.2018 - kill -0 <pid> (checking if "process exists") can fail with Operation not permitted.

17.12.2018 - seteuid and setegid instead of setuid and setgid (if you want to change back to root later).

29.03.2019 - If you need to know which user called sudo [command] you can read the SUDO_UID and SUDO_GID environment variables.

23.06.2019 - console.log() in node may leak memory.

23.06.2019 - To test network speed use pv /dev/zero | nc -l PORT respectively nc IP PORT > /dev/null.

21.07.2020 - One can set PS1 with a script: PROMPT_COMMAND in bash or precmd() in ZSH.

30.08.2020 - JavaScript: ArrayBuffer is a fast array buffer. Needs a ''view'' to access/modify data. For example Uint8Array or Uint16Array.

General commands

• Switch directory: cd <path>
• Go back to previous directory: cd -
• List contents of directory: ls
• List contents of path: ls <path>

GIT

• Init repo: git init

• Add file: git add <filename>

• Remove file: git rm [-r] <filename>

• Remove file without deleting it from disk: git rm --cached <filename>

• Show repo status: git status

• Commit changes: git commit

• Discard changes: git reset --hard HEAD

• Create branch: git branch <name>

• Switch branch: git checkout <name>

• Merge into current branch: git merge --no-ff <name>

• Pushing tags: git push origin tag-name

• Removing tags on origin: git push :refs/tags/tag-name.

• Removing tags locally: git tag -d tag-name.

• Show diff between two branches or commits: git diff <1> <2>.

• Show diff between current HEAD and last commit: git diff HEAD^.

• Nuke repo: rm -r .git

VIM

• Open file: vim <filename>

• Go to insert mode: i

• Erase character: x

• Erase until end of line: d$

• Erase word: dw or de

• Discard changes: :q!

• Save changes: :wq