JPNAS.NET / Cheat Sheets

🐧 Linux Command Line

The commands I use most on Linux servers and desktops – files, searching, permissions, processes, packages, services and logs. Examples are for Debian and Ubuntu; most work everywhere.

Open in the interactive Cheat Sheets

Moving around and files

pwd	Show the folder you are in.
ls -lah	List all files, also hidden ones, with sizes in KB/MB.
cd ~ cd - cd ..	Go to your home folder / back to the previous folder / one level up.
mkdir -p projects/site/img	Make a folder, with all missing parent folders.
cp -r source/ target/	Copy a folder with everything in it.
mv old.txt new.txt	Rename or move a file.
rm file.txt rm -r folder/	Delete a file / a folder. There is no recycle bin – check twice.
ln -s /mnt/nas/photos ~/photos	Make a shortcut (symbolic link).

Reading and searching

less file.log	Read a long file. Space = next page, / = search, q = quit.
head -n 20 file tail -n 50 file	The first 20 / last 50 lines.
tail -f /var/log/syslog	Follow a log live as new lines are written. Ctrl+C to stop.
grep -rni "error" /etc/nginx/	Search for text in all files of a folder, ignoring case, with line numbers.
find . -name "*.log" -mtime +7	Find .log files older than 7 days in this folder and below.
du -sh * | sort -h	How big is each folder here, smallest to biggest.
df -h	Free space on all disks.

Permissions and users

sudo command	Run one command as administrator (root).
chmod +x script.sh	Make a script executable.
chmod 644 file chmod 755 folder	Usual rights: owner can write, others only read.
sudo chown -R jernej:jernej folder/	Change the owner of a folder and everything in it.
whoami id	Who am I, and in which groups.
sudo adduser name sudo usermod -aG sudo name	Add a user / give them sudo rights.

Processes and system

htop	Live list of processes, CPU and memory (top if htop is not installed).
ps aux | grep nginx	Find a running process by name.
kill 1234 kill -9 1234	Ask a process to stop / force it to stop.
free -h	Memory and swap use.
uname -a cat /etc/os-release	Kernel version / which Linux this is.
lsblk -f	All disks and partitions with file systems.
uptime	How long since the last restart, and the load.

Packages (Debian, Ubuntu, Mint)

sudo apt update && sudo apt upgrade	Refresh the package list and install all updates.
apt search name	Find a package.
sudo apt install name	Install a package.
sudo apt remove name sudo apt autoremove	Remove a package / remove packages nobody needs any more.
sudo dnf upgrade	The same on Fedora.

Services and logs (systemd)

systemctl status nginx	Is the service running, and its last log lines.
sudo systemctl restart nginx	Restart a service, for example after changing its settings.
sudo systemctl enable --now nginx	Start a service now and at every boot.
systemctl --failed	Which services failed to start.
journalctl -u nginx -f	Follow the log of one service live.
journalctl -b -p err	All errors since the last boot.

Archives

tar -czf backup.tar.gz folder/	Pack and compress a folder.
tar -xzf backup.tar.gz	Unpack it here.
zip -r archive.zip folder/ unzip archive.zip	The same with .zip, for sending to Windows users.

Shell tricks

Tab	Complete a command or file name. Press twice to see all options.
Ctrl+R	Search through the commands you typed before.
sudo !!	Repeat the last command with sudo – when you forgot it.
command > file.txt command >> file.txt	Write the output to a file / add it to the end.
command1 | command2	Send the output of one command into the next.
Ctrl+C Ctrl+D	Stop the running command / log out of the shell.