System Administration

Useful commands for managing systems.

Linux / Unix

General

What's in this section?

These are commands you might find on any Linux, BSD, or even embedded systems.

w             # Show who's logged in, what they're doing
last | head   # List of last logged in users

Systemd

Systemd Commands

systemd-analyze may be used to determine system boot-up performance statistics and retrieve other state and tracing information from the system and service manager, and to verify the correctness of unit files. It is also used to access special functions useful for advanced system manager debugging.

systemd-analyze security [<unit>]  # Reviews sandbox settings of units, calculates risk score

Systemd *ctl Commands

Pattern: all *ctl tools share status, list, and tab-completion on unit/resource names.
Some commands use --json=[short|pretty] (hostnamectl, networkctl, etc) or -o json (journalctl) to dump the output to JSON
Some commands use --no-pager to dump results to stdout instead of a pager
Add -l to most commands to avoid truncated output.

systemctl - Service/unit management

systemctl status [<unit>|<pid>]  # Runtime status + latest journal logs
systemctl list-units [--failed]  # List units systemd has loaded in memory
systemctl list-timers            # All timers in memory, orderd by next run time
systemctl cat <unit>             # Cat the systemd unit file
systemctl show <unit>            # Shows low-level properties of units
systemctl is-active <unit>       # Returns true if the unit is active
systemctl is-enabled <unit>      # Returns true if the unit is enabled
systemctl is-failed <unit>       # Returns true if the unit has failed

journalctl - Log viewer

journalctl -b [<id>]             # Show logs from "BOOT_ID=<id>" or current boot if none
journalctl -u <unit> -f          # Tail a systemd service unit in real time
journalctl --since "10 min ago"  # Search by time
journalctl -p err                # Show errors only
journalctl <args>  --no-pager    # Print to stdout, not to a pager
journalctl <args>  -o json       # JSON output

hostnamectl - System hostname data

hostnamectl                       # Show hostname and device details (virtualization, chassis info, etc)
hostnamectl hostname <hostname>   # Set the hostname
hostnamectl <args> --json=pretty  # JSON oputput

networkctl - systemd-networkd status (only complete if networkd is running)

networkctl                       # Overview
networkctl status [<iface>]      # Overview + details
networkctl reload                # Reload .netdev and .network files

resolvectl - DNS data (only sees systemd-resolved and resolvconf info)

resolvectl status                # Show DNS settings currently in effect
resolvectl statistics            # DNSSEC status, resolution and validation stats
resolvectl query <hostname>      # Can use --type= or --class= to resolve records
resolvectl flush-caches          # Flush all local caches

timedatectl - Timezone, NTP data

timedatectl status                # Current time, timezone, NTP sync status
timedatectl list-timezones        # Lists all available timezone options
timedatectl set-timezone <tz>     # Sets timezone
timedatectl set-ntp <true|false>  # Enable or disable existing time synchronization service

loginctl - Session/user/seat management

loginctl list-sessions           # List current sessions
loginctl show-session <id>       # Show details of a session
loginctl lock-session <id>       # Locks a session
loginctl unlock-session <id>     # Unlocks a session
loginctl terminate-session <id>  # Kills all processes and deallocates resources of a session

coredumpctl - Retrieve and process core dumps

coredumpctl list                 # Lists a table of core dumps captured in the journal
coredumpctl info <pid|exe>       # Show details about <pid|exe>'s last core dump
coredumpctl debug <exe>          # Invoke gdb on <exe>'s last core dump

machinectl - VM / container management (sudo apt install systemd-containers)

machinectl list                  # List all active machines
machinectl list -o json          # JSON output
machinectl shell <machine>       # Open an interactive shell within <machine>
machinectl status <machine>      # Shows runtime status and journal log of <machine>

Xorg

TODO

Mirror Wayland commands here if possible

Wayland

Wayland and modern Linux systems may use systemd-logind to handle sessions and power / suspend decisions. acpid may still be present on some systems, but is more of a legacy component that's been replaced by logind.

Confirm you're on wayland:

echo $XDG_SESSION_TYPE

Get a list of sessions:

loginctl session-status

Dump the system's default session configuration:

loginctl show-session

List all system power action inhibitors; in other words, what-does-what when a poweroff / suspend / or hibernate request takes place.

systemd-inhibit --list