Linux User & File Management
Last modified: 2023-01-20
User Management
# List all users
cat /etc/passwd
cat /etc/shadow
# Add users
useradd <new-user>
useradd <new-user> -p <new-password>
# Delete users
deluser <user>
# Set passwords - stored in "/etc/shadow"
passwd <user>
Allow Users to Run Commands as Root Privilege
Add users to the “sudo” group.
usermod -a -G sudo <user>
# Check the permissions
su <user>
sudo -l
Group Management
# List all groups
cat /etc/group
# List groups where the specific user in
groups
groups <user>
# Create a new group
groupadd <new-group>
# Delete a group
groupdel <group>
# Add an user to a group
# -a: append the user to the specific group
# -G: group
usermod -a -G <group> <user>
# Change the user's primary group
# -g: gid
usermod -g <group> <user>
File Management
Change Owners of Files/Directories
# User only
chown <user> <file-name>
chown <user> <dir-name>
# -R: Recursive
chown <user> -R <dir-name>
# Group only
chown :<group> <file-name>
chown :<group> <dir-name>
# User and group
chown <user>:<group> <file-name>
chown <user>:<group> <dir-name>
Change Permissions of Files/Directories
# read+write+execute for an owner
chmod 700 sample.txt
chmod u+rwx sample.txt
# read+write+execute for a group
chmod 070 sample.txt
chmod g+rwx sample.txt
# read+write+execute for other users
chmod 007 sample.txt
chmod o+rwx sample.txt
# read+write+execute for all users
chmod 777 sample.txt
chmod a+rwx sample.txt
# read+write for an owner
chmod 600 sample.txt
SUID/GUID of Files/Directories
# SUID for an owner
chmod u+s sample.txt
# GUID for a group
chmod g+s sample.txt
