Linux Command Reference
Quick reference for sysadmin commands that are easy to forget. All commands tested on Ubuntu 22.04+.
| Command |
Description |
hostname |
Show the hostname |
head -n 1 /etc/os-release |
Show OS name and version |
uname -a |
Kernel version, architecture, hostname |
cat /proc/cpuinfo |
CPU details |
lspci -tv |
List all PCI devices |
lsusb -tv |
List all USB devices |
lsmod |
List loaded kernel modules |
env |
List all environment variables |
Resources
| Command |
Description |
cat /proc/loadavg |
System load averages (1, 5, 15 min) |
free -h |
RAM and swap usage |
df -h |
Disk usage per filesystem |
du -sh <dir> |
Size of a directory |
fdisk -l |
List all partitions |
swapon -s |
Show active swap partitions |
Networking
Modern tools
ifconfig and netstat are deprecated. Ubuntu 18.04+ uses ip and ss from the iproute2 suite, which is installed by default.
| Deprecated |
Modern replacement |
Description |
ifconfig |
ip a |
Show all interfaces and IPs |
ifconfig eth0 |
ip a show eth0 |
Show a specific interface |
route -n |
ip route |
Show routing table |
netstat -antp |
ss -antp |
All active connections with PID |
netstat -tulpn |
ss -tulpn |
Listening TCP/UDP sockets |
Services (systemctl)
| Command |
Description |
systemctl list-units |
List all active units |
systemctl list-units -a |
List all units including inactive |
systemctl list-units -a --state=inactive |
List only inactive units |
systemctl status <service> |
Status of a specific service |
journalctl -u <service> -f |
Follow logs for a service |
Users
| Command |
Description |
w |
Who is logged in and what they are doing |
last |
Login history |
crontab -l |
List cron jobs for the current user |
cut -d: -f1 /etc/passwd |
List all user accounts |
cut -d: -f1 /etc/group |
List all groups |
id <user> |
Show UID, GID, and group memberships |
APT Package Management
| Command |
Description |
update |
Refresh package index from sources |
upgrade |
Upgrade all installed packages |
install <pkg> |
Install a package |
remove <pkg> |
Remove a package (keep config files) |
purge <pkg> |
Remove a package and its config files |
autoremove |
Remove packages no longer needed |
dist-upgrade |
Upgrade with dependency resolution (safe) |
full-upgrade |
Upgrade including package removals if needed |
check |
Check for broken dependencies |
clean |
Remove cached package files |
show <pkg> |
Show package details |
list --installed |
List all installed packages |