linux command reference

This reference provides an overview of essential Linux commands for file management, process control, networking, system information, and more. It serves as a quick guide for both beginners and experienced users.

tip: this page is dense—use your browser search for keywords like “networking”, “systemctl”, “journalctl”, “/etc/fstab”, “usb devices”, “new disk”, “burning cd/dvd” to jump fast.

file and directory commands

file permissions and ownership

process management

networking commands

usb devices

configure interfaces

# Temporary (until reboot)
ip addr add 192.0.2.10/24 dev eth0
ip link set eth0 up
ip route add default via 192.0.2.1

# Debian/Ubuntu classic (/etc/network/interfaces)
auto eth0
iface eth0 inet static
  address 192.0.2.10/24
  gateway 192.0.2.1
  dns-nameservers 1.1.1.1 9.9.9.9

# Netplan (Ubuntu 22.04+, /etc/netplan/01-net.yaml)
network:
  version: 2
  ethernets:
    eth0:
      dhcp4: false
      addresses: [192.0.2.10/24]
      gateway4: 192.0.2.1
      nameservers:
        addresses: [1.1.1.1, 9.9.9.9]
# apply: netplan apply

# RHEL/CentOS ifcfg (/etc/sysconfig/network-scripts/ifcfg-eth0)
DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.0.2.10
PREFIX=24
GATEWAY=192.0.2.1
DNS1=1.1.1.1
DNS2=9.9.9.9
# restart: nmcli con reload && nmcli con up eth0

# systemd-networkd (/etc/systemd/network/10-eth0.network)
[Match]
Name=eth0
[Network]
Address=192.0.2.10/24
Gateway=192.0.2.1
DNS=1.1.1.1 9.9.9.9
# reload: systemctl restart systemd-networkd

system information

package management

Debian/Ubuntu-based Systems (using apt):

Red Hat/CentOS-based Systems (using yum or dnf):

compression and archiving

user and group management

disk management

provision a new disk (quick flow)

# 1) Identify the disk
lsblk -fp           # shows devices, fs type, UUIDs

# 2) Partition (example: GPT, one partition)
sudo parted /dev/sdb -- mklabel gpt
sudo parted /dev/sdb -- mkpart primary ext4 0% 100%

# 3) Make filesystem
sudo mkfs.ext4 /dev/sdb1

# 4) Mount temporarily
sudo mkdir -p /mnt/data
sudo mount /dev/sdb1 /mnt/data

# 5) Add to /etc/fstab (use UUID for stability)
UUID=$(blkid -s UUID -o value /dev/sdb1)
echo \"UUID=${UUID}  /mnt/data  ext4  defaults  0 2\" | sudo tee -a /etc/fstab
sudo mount -a   # verify fstab works

# 6) Permissions example
sudo chown -R $USER:$USER /mnt/data

/etc/fstab examples

# UUID recommended for stable devices
UUID=1111-2222  /           ext4  defaults              0 1

# NFS
192.0.2.20:/export/media  /mnt/media  nfs4  rw,_netdev,hard,intr  0 0

# SMB/CIFS (needs cifs-utils)
//fileserver/share  /mnt/share  cifs  credentials=/root/.smbcred,iocharset=utf8,vers=3.0,_netdev  0 0
# /root/.smbcred:
# username=alice
# password=secret
# domain=WORKGROUP

# tmpfs (RAM disk)
tmpfs  /mnt/ramdisk  tmpfs  size=1G,noexec,nodev,nosuid  0 0

# Bind mount
/var/log  /mnt/logcopy  none  bind  0 0

burning cd/dvd images

# Create ISO from folder
genisoimage -o image.iso -R -J /path/to/folder

# Verify ISO checksum
sha256sum image.iso

# Burn ISO to CD/DVD (wodim/growisofs)
wodim -v dev=/dev/sr0 speed=8 image.iso
# or for DVD/BD:
growisofs -dvd-compat -Z /dev/sr0=image.iso

# Erase rewritable media
wodim dev=/dev/sr0 blank=fast

# Verify disc
dd if=/dev/sr0 bs=1M | sha256sum

systemctl cheats

journalctl

system control and shutdown

environment variables and shell

text processing

redirection and pipes

Use redirection and pipes to control input and output:

• > - Redirect output to a file (overwrite).
• >> - Redirect output to a file (append).
• < - Redirect input from a file.
• | - Pipe the output of one command as input to another.
• 2>&1 - Redirect standard error to standard output.

examples

# Redirect output to a file
ls -l > filelist.txt

# Append output to a file
echo "New line" >> file.txt

# Redirect error messages to a file
command 2> error.log

# Pipe output to another command
ps aux | grep apache

# Suppress output
command > /dev/null 2>&1

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