Linux commands

Largest items in the current directory

Lists the 10 largest files and directories here (dotfiles excluded).

du -hs * | sort -rh | head -10

Find files over 100 MB

Finds files over 100 MB on the root filesystem, largest first.

sudo find / -xdev -type f -size +100M -exec du -h {} + 2>/dev/null | sort -rh | head -20

Tail systemd service logs

Follows journalctl logs for a service in real-time.

journalctl -u <service-name> -f

Stop the process listening on a port

Sends SIGTERM to the process listening on a TCP port.

Caution. Use kill -9 only if the process ignores SIGTERM: -9 skips its shutdown and cleanup.

kill $(lsof -t -i:<port> -sTCP:LISTEN)

Find the processes using the most CPU

Lists the top 10 processes consuming the most CPU.

ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head -11

Search string recursively

Searches for a string inside all files in a directory.

grep -rnw '/path/to/somewhere/' -e 'pattern'

Create soft symlink

Creates a symbolic link pointing to a target file or directory.

ln -s /path/to/target /path/to/link

Set permissions on directories only

Recursively changes permissions of directories only (leaving files untouched).

find . -type d -exec chmod 755 {} \;

Print specific columns with awk

Prints only the 3rd and 5th columns of a space-separated file.

awk '{print $3, $5}' data.txt

Find and replace in a file with sed

Replaces 'old-string' with 'new-string' inline in a file.

sed -i 's/old-string/new-string/g' config.yaml

GNU sed. On macOS, use sed -i '' instead of sed -i.

Delete log files older than 30 days

Finds .log files older than 30 days under /var/log and deletes them.

Caution. Deletes files permanently. Run it once without -delete to see the list first.

sudo find /var/log -type f -name "*.log" -mtime +30 -delete

Sync directories securely

Uses rsync to synchronize two directories over SSH, showing progress.

rsync -avz --progress /local/dir/ user@remote:/remote/dir/

Check free memory

Shows total, used and available memory in human-readable units.

free -h

Check disk space

Shows filesystem disk space usage and types.

df -Th

Find and change owner

Finds files owned by root and changes them to another user.

Caution. Changes ownership of everything it matches. Check the path first; run against / it can break the system.

find /path -user root -exec chown user:group {} +

Create tar.gz archive

Compresses a directory into a tarball.

tar -czvf archive.tar.gz /path/to/dir

Watch a command output

Runs a command repeatedly every 2 seconds, refreshing output.

watch -n 2 'kubectl get pods'

List listening ports and their processes

Shows TCP and UDP sockets in the LISTEN state with the owning process. The modern replacement for netstat -tulnp.

sudo ss -tulpn

List block devices

Shows all block devices (disks, partitions) in a tree view.

lsblk -f

Enable service on boot

Enables a systemd service to start automatically on boot.

sudo systemctl enable <service-name>

Search command history

Searches your bash history for a specific command.

history | grep <keyword>

Edit cron jobs

Opens the crontab editor to schedule recurring tasks.

crontab -e

Create a new user

Creates a new system user with a home directory.

sudo useradd -m -s /bin/bash <username>

Check system uptime and load

Shows how long the system has been running plus load averages.

uptime

View kernel messages

Shows kernel ring buffer messages, useful for hardware/driver debugging.

sudo dmesg --level=err,warn -T | tail -30

Extract tar.gz archive

Extracts a compressed tarball archive to the current directory.

tar -xzvf archive.tar.gz