Linux commands

Files and folders#

Where am I, what's here#

Command	Does
`pwd`	Show the folder you're in
`ls`	List files
`ls -la`	List everything, including hidden files (names starting with `.`), with details
`ls -lh`	Details with readable sizes (K, M, G)
`cd /srv/files`	Go to a folder
`cd ~` or just `cd`	Go home
`cd ..`	Go up one folder
`cd -`	Go back to the previous folder
`tree -L 2`	Show folders as a tree, 2 levels deep (`sudo apt install tree`)

Command	Does
`cat FILE`	Print the whole file
`less FILE`	Scroll through it (arrows, `Space` for next page, `/word` to search, `Q` quits)
`head -20 FILE`	First 20 lines
`tail -20 FILE`	Last 20 lines
`tail -f FILE`	Keep showing new lines as they're added (`Ctrl`+`C` stops)
`wc -l FILE`	Count the lines

nano FILE              # your own files
sudo nano /etc/FILE    # system settings

Before editing a system file, keep a copy

sudo cp -a /etc/ssh/sshd_config /etc/ssh/sshd_config.bak. -a keeps the owner and permissions.

Command	Does
`mkdir NAME`	New folder
`mkdir -p a/b/c`	New folder with all the parent folders
`touch FILE`	New empty file
`cp FILE COPY`	Copy a file
`cp -r FOLDER COPY`	Copy a folder with everything inside
`cp -a SOURCE DEST`	Copy and keep owner, permissions and dates (best for backups)
`mv OLD NEW`	Rename, or move to another folder
`mv -n OLD NEW`	Same, but never overwrite an existing file
`rm FILE`	Delete a file (no recycle bin)
`rm -r FOLDER`	Delete a folder and everything inside
`rm -i FILE`	Ask before each delete

rm has no undo

Check the path twice. Never run rm -rf with sudo on a path you copied from somewhere else.

Command	Does
`find /srv/files -name "*.pdf"`	All PDFs under a folder
`find . -iname "report"`	Name contains "report" (`-iname` ignores upper/lower case)
`find /srv/files -size +1G`	Files bigger than 1 GB
`find ~ -mtime -1`	Changed in the last day
`grep "word" FILE`	Lines containing a word
`grep -rn "word" /etc/ssh/`	Search all files in a folder, with line numbers
`grep -i "error" FILE`	Ignore upper/lower case

Command	Does
`tar -czf backup.tar.gz FOLDER`	Pack a folder into one compressed file
`tar -tzf backup.tar.gz`	List what's inside, without unpacking
`tar -xzf backup.tar.gz -C /tmp/test`	Unpack into a folder
`gpg --symmetric FILE`	Encrypt with a passphrase (makes `FILE.gpg`)
`gpg -d FILE.gpg > FILE`	Decrypt
`sha256sum FILE`	Fingerprint of a file (to check copies are identical)