> For the complete documentation index, see [llms.txt](https://refdocs.buymeasoda.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://refdocs.buymeasoda.com/unix/user-file-and-group-permissions.md).

# User, file and group permissions

## Info

Show all groups a user belongs to

```
groups <user>
```

Show primary groups for user

```
id <user>
```

## Sudo

Perform a command as the super user

```
sudo <command>
```

## Switch users

Switch to specific user

```
su <user>
```

Switch to root or specific user and load user profile (`CTRL + d` to exit user mode)

```
su -
su - <user>
```

## Managing users

Create a new user

```
adduser <username>
```

Change password for active user

```
passwd
```

## File permissions

Change file mode and access control

```
chmod <permissions> <file>
```

Permission types

```
r = read
w = write
x = execute
```

Numerical values

```
r = 4
w = 2
x = 1
```

Permission groups

```
u = user
g = group
o = other
a = all (sets u, g and o)
```

### Set permissions with assigment

Set user to rwx, group to rw and other to r

```
chmod u=rwx,g=rw,o=r <file>
```

Set u to rwx, group and other to r

```
chmod u=rwx,go=r <file>
```

### Alter some permission with plus and minus

Add write permissions to user group

```
chmod g+w <file>
```

Remove read and write permission from other group

```
chmod o-rw <file>
```

Add execute for user, remove write for group, remove rwx for other

```
chmod u+x,g-w,o-rwx
```

### Use -R to set permissions recursively

Set group to read and write for the directory and all sub files and folders

```
chmod -R g=rw <dir>
```

### Set user / group for new files

Set group automatically when creating new files within `<dir>` via the `g+s` SETGID (SET Group ID) flag

```
chmod g+s <dir>
```

Remove setting group automatically for new files within `<dir>` by removing set group flag

```
chmod g-s <dir>
```

## Managing groups and owners

List available groups

```
less /etc/group
```

Modify a user (usermod) and add (-a) them to a group (-G)

```
usermod -a -G <group> <username>
```

Change file group associated with the file permissions

```
chgrp <group> <file>
```

Change file owner

```
chown <user> <file>
```

## Cleaning up file permissions

Find files with permission set to 777 and change them to default 644

```
find . -type f -perm 777 -print0 | xargs -0 chmod 644
```

Find directories with permission set to 777 and change them to default 755

```
find . -type d -perm 777 -print0 | xargs -0 chmod 755
```

Unlock all locked files found under the current directory

```
chflags -R nouchg *
```