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Linux Command-line Basics#

Basics of Basics#

  • ls list files
  • ls -l list files with details
  • ls -la list all files with details including hidden files
  • cd change directory
  • cd .. move out / up current directory by one layer
  • cd ~ change to home Directory
  • pwd print current working directory

Create/Modify files and folders#

  • touch <filename> create a new file
  • mkdir <dirname> make a new directory (folder)
  • rm <filename(s)> remove file(s)
  • rmdir <dirname(s)> remove empty directory(s)
  • rm -rf <dirname(s)> remove directory(s) recursively
  • cp copy files(s)
  • mv <filename> <new filename> rename a file
  • mv <filename(s)> <target path> move file(s) to target path
  • nano <filename> launch nano text editor to edit file content

Check system information#

  • lsb_release -a check ubuntu version
  • echo print function
  • sudo reboot reboot
  • sudo shutdown -h now shutdown now
  • ifconfig
  • iwconfig
  • ping <domain name or ip address>
  • top show processes; use q to quit
  • uname -a check machine info
  • lsusb list usb
  • lspci list pci

User & Permissions#

User and groups#

Create a new user with home directory

sudo useradd -m username

List all users

less /etc/passwd
# or
users

List all groups

less /etc/group
# or
groups

List all groups that a specific user belongs to

groups USER
# or
id USER

List all users in a specific group

getent group GROUP

Add a user to a group

usermod -aG GROUP USER
  • New group will be one of the user's secondary groups

Change a user's primary group

usermod -g GROUP USER

User password#

Change the current user's password

passwd

Change any user's password with sudo privileges

sudo passwd USER

Switch user#

  • sudo -i becoming root user (require current user password)
  • su - become root user (require root password)
  • su [username] switch to user

Ref: Difference between sudo -i and su -

File Permissions#

UNIX System Permissions

Example: 

drwx------   5 markhuang  staff   160B Jan 13 11:13 .ssh
lrwxr-xr-x   1 markhuang  staff    40B Jan  8 17:41 .tmux.conf -> ./dotfiles/tmux/tmux.conf
-rw-------   1 markhuang  staff   797B Jan  9 16:39 .viminfo

  • First char: d/l/- stands for dir/link/file
  • following 3 chars: r/- + w/- + x/- represent Read,Write,Execute permission for owner user.
  • following 3 chars: r/- + w/- + x/- represent Read,Write,Execute permission for owner group.
  • following 3 chars: r/- + w/- + x/- represent Read,Write,Execute permission for other user.

Change owner for all files inside a folder

sudo chown USER[:GROUP] FILE(s)

# e.g. Change the owner and group of example.txt to user jack and group jack
sudo chown jack:jack example.txt

Change user permission of a file

chmod NEW_PERMISSIONS FILE

# e.g. Add execution permission for owner to example.sh
chmod u+x example.sh
# e.g. Add execution permission for owner and group to example.sh
chmod ug+x example.sh
# e.g. Remove execution permission for everyone to example.sh
chmod a-x example.sh
# e.g. Add read permission for everyone to example.sh
chmod a+r example.sh
# e.g. Change the permissions of example.sh to `rwxrwxrwx`
chmod 777 example.sh
  • u: permission for owner user
  • g: permission for owner group
  • o: permission for other user
  • a: permission for all
  • ugo: permission for all
  • +: add permission
  • -: remove permission
  • 777: permission equivalent to rwxrwxrwx
  • 644: permission equivalent to rw-r--r--

Disk#

Check disk utilization#

df -h
  • -h for "Human-readable" output

Example:

df -x tmpfs -x squashfs -x devtmpfs -x vfat -hT
  • -x or --exclude-type for excluding certain file systems Type
  • -T for printing file system type

Check file/folder size#

du -sh {dir}
Example:

du -sh ./*
  • -s for "specified" file/dir only
  • -h for "Human-readable" output

Working with Files and Folders#

  • mkdir new_folder_name make directory (create a new folder)
  • rmdir some_folder remove a empty folder
  • rm -rf some_folder remove a folder and everything inside

More about removing directories: How to Remove (Delete) Directory in Linux

  • touch example.txt create a new file
  • nano example.txt edit a file using the nano text editor
  • vim example.txt edit a file using the vim text editor
  • cat example.txt print out file content
  • rm example.txt remove a file (delete a file)

move a file 

mv [current path to file] [new path to file]
mv example.txt ~/Desktop/example.txt

rename a file 

mv [current file name] [new file name]
mv example.txt example_renamed.txt

copy a file 

cp [current path to file] [new path to file]
cp example.txt example_copy.txt

Copy files between machines#

scp also supports autocompletion for remote files and directories if you have existing SSH connection to the remote machine.

secure copy to remote machine

scp [local file] [remote user]@[remote address]:[remote path]

scp example.json root@178.128.22.33:/home/root/example

secure copy from remote machine

scp [remote user]@[remote address]:[remote file] [local path]

scp root@178.128.22.33:/home/root/example.json .

When copying a good number of files

  • Consider using a simpler encryption algorithm
  • Consider using rsync instead of scp
  • Consider using parallel-scp and parallel-rsync