System information

The following are common and useful Linux commands and utilities for managing and finding system information.

1 System information, performance and utilities

Command	Function
arch	Display system architecture (e.g., x86_64)
cal	Displays the current month's calendar; can also show calendar of any specified month or year (years 0-9999)
cat /etc/rel	Show detailed OS and release version information
cat /etc/redhat-release	Show which version of Redhat installed
date	Display the current system date and time
date -d	Print formatted date
free -h	Display free and used memory (in human readable format)
free -m OR -g	Display free and used system memory in megabytes or gigabytes, respectively
hostname	Display the system's hostname
hostname -I	Display the host IP addresses
hostnamectl	Display hostname & operating system information, e.g., kernel, and release version
hostnamectl new-name	Change hostname
htop	Interactive process viewer (alternative to top)
im-config	Check text input method setup (e.g., ibus or fcitx for inputting non-Western languages)
iostat 1	Outputs I/O (Input/Output) statistics.
last reboot	Display system reboot history
lsb_release -a	Display operating system distributor ID, description, release, and codename.
lslogins	Display information on known users
lsof	List all open files on the system
lsof -u user	List files opened by user
neofetch OR screenfetch	Display OS, desktop environment, basic system info, & OS logo (requires installation)
mpstat 1	Outputs processor-related statistics.
route -n	Display kernel IP routing table
tail 100 /var/log/messages	Display the last 100 syslog messages (using /var/log/syslog for Debian based systems.)
tcpdump -i eth0	Capture and display all packets on interface eth0
tcpdump -i eth0 'port 80'	Monitor all traffic on port 80 (HTTP)
top	Display and manage the top processes
uname	Print system information
uname -a	Print a summary of information on the system, OS, kernel, and machine
uname -r	Display kernel version and release information
uptime	Shows how long the system has been active, and average load
vmstat -s	Detailed virtual memory statistics
vmstat 1	Display virtual memory statistics with constant updating
watch df -h	Execute "df -h" to view file system information, showing periodic updates

2 Hardware management

Command	Function
badblocks -s /dev/sda	Test for unreadable blocks on disk sda
badblocks dev -v	Search for bad sectors on device
badblocks dev -v > file	Search for bad sectors on device and save to a file
cat /proc/cpuinfo	More information about CPU e.g model, model, name, cores, vendor id
cat /proc/meminfo	More information about hardware memory, e.g., total and free memory
df	Display file system information
df -h	Display file system information in human-readable format
dmesg	Outputs the kernel ring buffer messages.
dmidecode	Outputs the system's hardware information on DMI/SMBIOS related to the BIOS.
free	Display system memory (RAM and swap); -h human readable; -m megabytes; -g gigabytes
free -h	Display free and used memory (in human readable format)
hdparm -i /dev/sda	Display data on a specified disk
hdparm -tT /dev/sda	Output read speed test performance for a disk
insmod	Install modular device drivers
iostat	Detailed information on CPU cores and devices (via sysstat)
iostat 1	Real-time (constantly updating) iostat data
lp -d lp -P	Identify name of printer
lp -nc, lpr c	Print c copies of a file
lpq	Displays items in print cue
lpr file	Print file to the printer
lprm file	Cancel print jobs
lsblk	Display information on a system’s block devices
lscpu	Detailed CPU information
lshw	Outputs the system's hardware configuration information.
lslocks	Display system locks
lsmem	Display memory usage information
lsmod	List kernel modules that are currently loaded
lsof	Display currently open files
lspci -tv	Display a system's PCI devices.
lsusb	Display USB ports and devices
lsusb -tv	Display system's USB devices.
setxbmap	Change to different keyboard setup
top, htop	Display memory usage and processes
vmstat -s	Detailed virtual memory statistics
vmstat 1	Display virtual memory statistics with constant updating
xev	Interactive program for finding key bindings and codes for keyboard keys
xmodmap -pke	Display list of keyboard key codes (keymaps)
xmodmap -pm	Display list of modifier key mappings
xmodmap .Xmodmap	Update Xmodmap file of keyboard settings (in user directory)

3 Machine state

Command	Function
reboot	Restart the system
shutdown -f	Do a fast shutdown
shutdown -h now	Shut down the system now
shutdown -r	Reboot the system; time argument is optional
shutdown -t time	Shutdown the system at a specified time, e.g., 11.00 for 11am
shutdown -t +#min	Shutdown within a specified number of minutes
shutdown message	Shutdown and broadcast a message

4 Important system directories and files

Command	Function
/etc	system-wide configuration files
/etc/release	OS and version information
/etc/bash.bashrc	Global config file for bash shell
/etc/group	Group information
/etc/hosts	Configuration for network hosts
/etc/inittab	Login and runlevel configuration
/etc/network/interfaces	Location of network interface information
/etc/networks	Configuration for networks
/etc/passwd	User account information
/etc/profile	Global environmental config files
/etc/redhat-release	OS information (for RHEL)
/etc/shadow	Where passwords are stored
/etc/skel	Skeleton and template home directory for new home directories
/etc/ssh/sshd_config ‘’OR’’ ssh_config	SSHD configuration file (e.g., to change assigned port numbers)
/etc/syslog.conf	Configuration for syslog logging daemon
/etc/systemd/system	Daemon config file and setup
/proc/cpuinfo	CPU info
/usr/share/X11/xkb/symbols/	Location of system keyboard keymaps
/var/log	System logs
/var/log/messages	System messages
/var/log/syslog	System logs
~/.bash_login	If ~/.bash_profile is not found, bash attempts to read this script
~/.bash_profile	User’s personal startup file
~/.bashrc	User config file for bash shell
~/.profile	User environmental config file
~/.profile	Profile file used by bash if .bash_profile and .bash_login do not exist
~/.XCompose	User-defined compose keys (for dead keys, compose keys)
alias	Show defined aliases
export VAR	Make a VAR available to child process
fuser	Show which processes are using a particular file, device, or system resource
fuser -m /dev/sda1	Show which processes are using a particular device
printenv	Print defined environmental variables

5 System init or runlevels

These are common init levels or runlevels in Unix based systems, though these may vary slightly among different distributions or operating systems. Users will generally do their work in Runlevel 5, which is the standard GUI runlevel.

Runlevel status or command	Function
Runlevel 0	System halt, for shutting down the system
Runlevel 1	Single-user mode (no GUI)
Runlevel 2	Multi-user mode without networking (or GUI)
Runlevel 3	X-server is loaded, for basic GUI elements; multi-user mode with networking (in command line interface)
Runlevel 4	User-definable mode
Runlevel 5	Full graphical environment; multi-user mode with networking and full GUI
Runlevel 6	Reboots for a system restart

6 Startup or login problems

Command	Function
loginctl unlock-session 2	Unlock a borked session from tty when normal login fails, or when the regular user session is borked
kquitapp5 plasmashell && kstart5 plasmashell	Kill and restart a borked KDE session from termianl without logging out
pkill -HUP -f "cinnamon --replace"	Kill and restart a borked Cinnamon desktop session from tty or terminal without logging out
sudo service mdm restart	Kill and restart a borked Cinnamon desktop session from tty or terminal without logging out