🖥️ tmux — Terminal Multiplexer
1
Install & Start a Session
tmux lets you run multiple terminals inside one window and keep them alive after you disconnect.
bash — Install
sudo apt update && sudo apt install -y tmux
bash — Start a named session
# Start a new session called "work" tmux new -s work
Inside tmux, every command starts with the prefix key
Ctrl+b: press Ctrl+b, release, then press the command key (e.g. Ctrl+b then d to detach).2
Detach & Reattach
Detach to leave a session running in the background — perfect for long jobs over SSH.
tmux keys — inside a session
Ctrl+b d # Detach (session keeps running after you disconnect SSH)
bash — From the shell
# List running sessions tmux ls # Reattach to the "work" session tmux attach -t work # Kill a session when you are done tmux kill-session -t work
3
Windows & Panes
Windows are like tabs; panes split one window into multiple terminals. All keystrokes are pressed after the Ctrl+b prefix.
tmux keys — inside a session
# --- Windows (tabs) --- Ctrl+b c # Create a new window Ctrl+b n # Next window Ctrl+b p # Previous window Ctrl+b 0-9 # Jump to window by number # --- Panes (splits) --- Ctrl+b % # Split vertically (left | right) Ctrl+b " # Split horizontally (top / bottom) Ctrl+b ←↑↓→ # Switch between panes with arrow keys Ctrl+b x # Close the current pane (or just type: exit)
🔄 rsync — Sync & Backup
4
Local Copy
The -a flag preserves permissions, timestamps and symlinks; -v is verbose.
bash
# Copy the CONTENTS of /src into /dest
rsync -av /src/ /dest/
Trailing slash matters:
/src/ copies the contents of src into dest, while /src (no slash) copies the directory itself into dest (creating /dest/src/).5
Over SSH
Add -z to compress data in transit and -e ssh to use SSH as the transport.
bash — Push (local → remote)
rsync -avz -e ssh /local/dir/ user@server:/remote/dir/
bash — Pull (remote → local)
rsync -avz -e ssh user@server:/remote/dir/ /local/dir/
6
Mirror with --delete (Dry-Run First)
Always preview a mirror with --dry-run before running it for real.
bash — Preview only
# Show what WOULD change — nothing is written
rsync -av --delete --dry-run /src/ /dest/
bash — Run for real
# Same command without --dry-run, with a progress bar
rsync -av --delete --progress /src/ /dest/
bash — Exclude files
# Skip a directory rsync -av --exclude='node_modules' /src/ /dest/ # Or read patterns from a file (one per line) rsync -av --exclude-from=excludes.txt /src/ /dest/
--delete is destructive: it removes any files in the destination that no longer exist in the source. Dest becomes an exact mirror of source — run the dry-run first every time.
⏰ cron — Scheduling
7
Edit the Crontab
Each user has their own crontab. Use crontab -e to edit it safely.
bash
# Edit your own crontab crontab -e # List your current cron jobs crontab -l # Edit another user's crontab (needs root) sudo crontab -e -u username
8
Cron Syntax & Examples
Five time fields, then the command to run.
crontab — Field layout
# ┌───────── minute (0-59) # │ ┌─────── hour (0-23) # │ │ ┌───── day of month (1-31) # │ │ │ ┌─── month (1-12) # │ │ │ │ ┌─ day of week (0-7, Sun=0 or 7) # │ │ │ │ │ # * * * * * command-to-run
crontab — Examples
0 3 * * * /path/script.sh # Every day at 3:00 AM */15 * * * * /path/script.sh # Every 15 minutes 0 9 * * 1-5 /path/script.sh # 9:00 AM, Mon–Fri @reboot /path/script.sh # Once at every boot @daily /path/script.sh # Once a day (midnight)
crontab — Log the output
# Redirect stdout AND stderr to a log file
0 3 * * * /path/script.sh >> /var/log/myjob.log 2>&1
9
System-Wide Cron & Logs
Beyond per-user crontabs, the system has drop-in locations and run-part directories.
bash — System cron locations
# Drop custom job files here (note the extra "user" field) /etc/cron.d/ # The main system crontab /etc/crontab # Scripts placed here run automatically: /etc/cron.daily/ # run once a day /etc/cron.weekly/ # run once a week /etc/cron.monthly/ # run once a month
bash — Check that jobs actually ran
# View cron activity via the journal journalctl -u cron # Or grep the syslog (older systems) grep CRON /var/log/syslog
cron runs with a minimal PATH (usually just
/usr/bin:/bin), so it won't find commands the way your login shell does. Use absolute paths in your scripts and cron lines, or set PATH= at the top of the crontab.