# Login as user
su - <USERNAME>
# Login as root
sudo -i
# Logout
CTRL + d # or exit
# Change password
sudo passwd <USERNAME># Guided user creation
adduser <USERNAME>
# Add sudo access
usermod -aG sudo <USERNAME>
# remove sudo access
sudo deluser <USERNAME> sudo
# Scripted user creation
useradd --uid <UID> --gid <GID> -m -s /usr/bin/zsh -d /var/www/<USERNAME> --password <PASSWORD> <USERNAME># Remove user
sudo deluser --remove-home <USERNAME>
# Check if user exists
id <USERNAME>
# Kill all processes by user
pkill -u <USERNAME>The root account is disabled by default in Ubuntu, so there is no root password, that's why su fails with an authentication error.
ls -l
# permission links user group size changed file
# -rwxrwxrwx 1 foo bar 45 Nov 13 22:51 script.js| Permission | Type | Owner | Group | Other | Meaning |
|---|---|---|---|---|---|
| -rwx------ | - (file) | rwx | --- | --- | File only the owner can read, write and execute. |
| drw-rw---- | d (directory) | rw- | rw- | r-- | Owner and group can read/write, others just read. |
# Change file owner
chown user:group file_name
# Add user to a group. Needs a logout
sudo usermod -a -G group user# Change file mode i.e. `rwx` permissions.
chmod
# Add EXECUTE permission to owner, group and others.
chmod +x FILE
# Add WRITE permission to just the owner.
chmod u+w FILE
# Remove read permission to other users.
chmod o-r FILEAdding permission one by one can get very tedious (9 commands), so instead, we can set the permissions by using octal numbers.
chmod 754 FILE| Owner | Group | Others | |
|---|---|---|---|
| Octal | 7 | 5 | 4 |
| Chars | rwx | r-x | r-- |
| Permission | Read, write, execute | Read, execute | Read |
A binary mask is used to determine the numbers. Add the column values for each 1 and the sum is the decimal number.
| Dec | Permission | RWX | Read (4) | Write (2) | Execute (1) | Decimal |
|---|---|---|---|---|---|---|
| 7 | Read, write, execute | rwx | 1 | 1 | 1 | 7 |
| 6 | Read, write | rw- | 1 | 1 | 0 | 6 |
| 5 | Read, execute | r-x | 1 | 0 | 1 | 5 |
| 4 | Read | r-- | 1 | 0 | 0 | 4 |
| 3 | Write, execute | -wx | 0 | 1 | 1 | 3 |
| 2 | Write | -w- | 0 | 1 | 0 | 2 |
| 1 | Execute | --x | 0 | 0 | 1 | 1 |
| 0 | No permissions | --- | 0 | 0 | 0 | 0 |