Linux Cheat Sheet

Links

“The art of command line” should have included most essential commmands. https://github.com/jlevy/the-art-of-command-line

“Linux Productivity Tools” by Ketan M. https://www.olcf.ornl.gov/wp-content/uploads/2019/12/LPT_OLCF.pdf

Plus all kinds of cheatsheets online. https://tmuxcheatsheet.com/

You would thank shellcheck.

My Tips

I don’t think there is any meaning memorising all the commands and options. I learn the commands when I use them. I forget if I don’t touch them for a long time.

On top of that, why would I bother when I have handy tools like tldr, cheat.sh and man.

The really important commands you should remember are:

brew install tlrc
tldr tar
# or
curl cht.sh/tar
# or
man tar

Commands

File

• grep <pattern> <file>
• zcat <file.gzip>
• zless <file.gzip>
• head/tail -n 10
• tail -f <file>
• scp <server:path> <dest>
• du -sh <path> | sort -h
• cat <file> | tr '\n' ';'
• sed tldr
• tee
• find . -maxdepth 1 -type f -exec wc -l {} \;
• cmd > log.txt 2>&1 redirect stderr and stdout to log.txt
• split --number 2 <file> Used one time when I have to split a 10G file into under 1G per file.

I can spend a section on sed and awk and more on find. But I will probably ask AI when I want to use them.

File permisson:

# user group other
-rwxrwxrwx
# directory
drwxrwxrwx

SSH

• ssh-keygen -t ed25519 -a 32 -f ~/.ssh/id_ed25519 -C "comment"

Bash

• set -euo pipefail exit immediately if a command exits with non-zero status.

• history

• Heredoc

  cat << EOF
  line 1
  line 2
  EOF

System

• top
• ps aux
• lsof -i :8080
• lsof -p <PID> | wc -l check number of file descriptors.
• lshw
• df
• free --human Show free memory
• uname -a details about the current machine and the operating system
• lsb_release -a
• uptime
• w Show who is logged on and what they are doing.
• hostname
• nohup <script.sh> &
• jobs
• kill <pid>
• sudo nvme smart-log <device>. Checking the SSD status. Probably the last thing to confirm when a database was down.
• systemctl status <service>

Network

• host <domain> <dns>
• ufw Uncomplicated Firewall
• ip addr
• dig example.com
• netstat -tuln

DNS file: /etc/resolv.conf

Notes

An inode stores all metadata about a file, except for the filename.

Hard links:

• Only link to a file, not a directory
• Can’t reference a file on a different disk/volume
• Links will reference a file even if it is moved
• Links reference inode/physical locations on the disk

Symbolic (soft) links:

• Can link to directories
• Can reference a file/folder on a different hard disk/volume
• Links remain if the original file is deleted
• Links will NOT reference the file anymore if it is moved
• Links reference abstract filenames/directories and NOT physical locations.
• They have their own inode