Quick explanations and common usages
Print system information (kernel, architecture, etc.).
uname
Kernel name (same as uname -s).
uname -r
Kernel release (version string).
uname -a
All available info (kernel, node, release, build, arch).
uname -m
Machine hardware name (e.g., x86_64, aarch64).
Show how long the system has been running and the load averages.
uptime
Classic output with current time, up time, users, load.
uptime -p
Pretty format (e.g., 'up 3 hours, 12 minutes').
uptime -s
System boot time (timestamp).
Display or set the system’s host name.
hostname
Print current host name.
hostname -I
Show all assigned IP addresses (space-separated).
hostnamectl
Show host metadata (Static/Pretty name, chassis, etc.).
sudo hostnamectl set-hostname myhost
Set persistent host name (requires sudo).
List reboot history using the wtmp log.
last reboot
Show each reboot event and its time range.
last -x | grep reboot
Include system runlevel changes, then filter reboots.
who -b
Alternative: show last boot time only.
Print or set the system date and time.
date
Current local date/time.
date -u
Current time in UTC.
date +"%Y-%m-%d %H:%M:%S"
Custom format (YYYY-MM-DD HH:MM:SS).
sudo date -s "2025-08-28 12:00:00"
Set date/time (requires sudo; use with care).
Control and query system clock/timezone (systemd-based distros).
timedatectl status
Show local time, UTC, RTC, NTP, timezone.
timedatectl list-timezones
List valid timezones.
sudo timedatectl set-timezone Europe/Berlin
Change timezone (requires sudo).
timedatectl timesync-status
Show network time sync (if available).
Display a calendar.
cal
Current month calendar.
cal -y
Whole year calendar.
cal 9 2025
Specific month and year (September 2025).
ncal -w
Alternative layout; show ISO week numbers.
Show who is logged in and what they’re doing; includes load and uptime.
w
Standard multi-line session summary.
w -h
Hide header (useful for scripts).
w -s
Shorter format without login/idle times.
Print the effective username of the current user.
whoami
Just the username; handy in scripts/prompts.
User information lookup (may need the 'finger' package installed).
finger
List logged-in users with details.
finger username
Show info for a specific user (gecos, shell, last login).
Print or control the kernel ring buffer (boot and hardware messages).
dmesg | less
View full kernel log with paging.
dmesg -T
Show timestamps in human-readable form.
dmesg | grep usb
Filter messages for USB devices.
Concatenate and print files. Often used to read system info in /proc or /sys.
cat /proc/cpuinfo
Detailed CPU information.
cat /proc/meminfo
Detailed memory statistics.
cat /etc/os-release
Distribution details.
List hardware information (requires root for full details).
sudo lshw
Full hardware summary.
sudo lshw -short
Compact summary of hardware.
sudo lshw -C disk
Show only storage devices.
List block devices (disks, partitions, mount points).
lsblk
Tree view of devices and mounts.
lsblk -f
Include filesystem info (UUID, type).
lsblk -o NAME,SIZE,TYPE,MOUNTPOINT
Custom output columns.
Display memory usage statistics.
free -h
Human-readable output (MB/GB).
free -m
Values in MB.
watch -n1 free -h
Refresh memory usage every second.
List PCI devices (graphics, network, etc.).
lspci
Basic list of PCI devices.
lspci -v
Verbose details.
lspci -nnk | grep -A3 VGA
Show GPU and kernel driver in use.
List USB devices connected to the system.
lsusb
Basic list of USB devices.
lsusb -v
Verbose info (needs sudo for full details).
lsusb -t
Tree view of USB hierarchy.
Dump hardware info from the system BIOS (requires root).
sudo dmidecode
Full dump of BIOS and hardware tables.
sudo dmidecode -t memory
Details about system RAM modules.
sudo dmidecode -t system
System vendor, product name, serial number.
Print user identity (UID, GID, groups).
id
Show UID, primary GID, and groups for current user.
id username
Show UID/GID/groups for another user.
Show who is currently logged in.
who
List logged in users and their terminals.
who -b
Show last system boot time.
Show login history (from /var/log/wtmp).
last
Full login/logout history of users.
last username
History for a specific user.
last -x
Include system shutdown/reboot records.
Show groups a user belongs to.
groups
Show groups for current user.
groups username
Show groups for another user.
Query the system user database (passwd file or NSS).
getent passwd
List all users.
getent passwd username
Show entry for a specific user.
Query the system group database.
getent group
List all groups.
getent group admin
Show entry for a specific group.
Create a new user account (implementation varies by distro).
sudo adduser newuser
Debian/Ubuntu style (interactive, sets password).
sudo useradd -m newuser
RedHat style (create with home directory).
Modify an existing user account.
sudo usermod -aG admin username
Add user to group 'admin' (append mode).
sudo usermod -s /bin/zsh username
Change user’s login shell.
Delete a user account.
sudo userdel username
Remove user but keep home directory.
sudo userdel -r username
Remove user and delete home directory.
Add or remove groups.
sudo groupadd admin
Create a new group named 'admin'.
sudo groupdel admin
Delete the group 'admin'.
Administer /etc/group (set or change group membership).
sudo gpasswd -a username group
Add user to a group.
sudo gpasswd -d username group
Remove user from a group.
List directory contents.
ls -l
Long format (permissions, owner, size, date).
ls -a
Show hidden files (dotfiles).
ls -lh
Human-readable sizes.
Print current working directory.
pwd
Show absolute path of current directory.
Create directories.
mkdir mydir
Create a single directory.
mkdir -p parent/child
Create parent and child directories recursively.
Remove files or directories.
rm file
Delete a file.
rm -r dir
Delete a directory and its contents.
rm -rf dir
Force remove directory (dangerous!).
Copy files or directories.
cp file1 file2
Copy file1 to file2.
cp -r dir1 dir2
Copy directory recursively.
Move or rename files/directories.
mv old new
Rename file or directory.
mv file dir/
Move file into directory.
Create empty files or update timestamps.
touch newfile
Create an empty file.
touch -m file
Update modification time.
View file contents.
cat file
Dump file contents to terminal.
more file
Page through file (space to scroll).
less file
Like more, but with better navigation.
View the beginning or end of a file.
head -n 20 file
First 20 lines.
tail -n 50 file
Last 50 lines.
tail -f logfile
Follow live appending log file.
Build and execute command lines from input.
cat list.txt | xargs rm
Remove files listed in list.txt.
find . -name '*.log' | xargs gzip
Compress all .log files.
Search for files and directories.
find . -name 'file.txt'
Find file in current directory (recursive).
find /path -type f -name '*.log'
Find all .log files under /path.
find /var -size +100M
Find files larger than 100 MB.
find /home -mtime -7
Find files modified in the last 7 days.
find . -name '*.txt' -exec grep -H 'pattern' {} \;
Find .txt files containing 'pattern'.
Find files using prebuilt database (faster than find).
locate filename
Search for file by name.
updatedb
Update database (requires sudo).
Search inside files by text patterns.
grep 'pattern' file
Search for text in file.
grep -r 'pattern' dir/
Search recursively in directory.
grep -i 'pattern' file
Case-insensitive search.
grep -n 'pattern' file
Show matching line numbers.
Report processes.
ps aux
Show all processes with user, CPU, mem, etc.
ps -u username
Show processes for a specific user.
ps -ef | grep nginx
Find a process by name.
Monitor running processes.
top
Dynamic view of processes.
htop
Improved top (color, interactive).
Send a signal to a process (default: TERM).
kill 1234
Terminate process with PID 1234.
kill -9 1234
Force kill process (SIGKILL).
pkill nginx
Kill all processes named nginx.
Show system load and uptime.
uptime
Load averages and uptime.
List process IDs by name.
pgrep sshd
Find PID of sshd.
pgrep -u user
Processes owned by a user.
Report filesystem disk space usage.
df -h
Human-readable disk usage.
df -i
Show inode usage.
Estimate file and directory space usage.
du -sh *
Sizes of folders/files in current directory.
du -ch
Summarize and show total.
Partition table manipulator (requires root).
sudo fdisk -l
List all partitions.
sudo fdisk /dev/sda
Edit partitions on disk sda.
Find mounted filesystems.
findmnt
List all mount points in a tree.
findmnt /home
Show what /home is mounted on.
Mount or unmount filesystems.
mount
Show currently mounted filesystems.
sudo mount /dev/sdb1 /mnt
Mount a device to a path.
sudo umount /mnt
Unmount from path.
Archive files.
tar -cvf archive.tar files/
Create archive from files/.
tar -xvf archive.tar
Extract archive.
tar -tvf archive.tar
List contents.
tar -czvf archive.tar.gz files/
Create gzip-compressed tar.
tar -xvzf archive.tar.gz
Extract gzip-compressed tar.
Compress/decompress files.
gzip file
Compress file (produces file.gz).
gunzip file.gz
Decompress .gz file.
Create and extract .zip archives.
zip archive.zip file1 file2
Zip multiple files.
unzip archive.zip
Extract zip archive.
Compress with high ratio.
xz file
Compress file to file.xz.
unxz file.xz
Decompress file.