umask

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Wat het doet

Programs create new files with 666 (rw for all) and new directories with 777. The umask removes bits from this: with umask 022, files get 644 and directories 755.

umask is a shell built-in: it changes only the current shell and its children. Make it permanent in ~/.bashrc (one user) or a file in /etc/profile.d/ (all users). Services use the UMask= setting in their systemd unit.

Zo schrijf je het

umask [-p] [-S] [MODE]

Opties 3

Meest gebruikt

MODE: The new mask, as a number (027) or in letters (u=rwx,g=rx,o=).
-S: Show the mask in letters (as the permissions that stay).
-p: Show it in a form you can use again as a command.

Voorbeelden 11

$ als gewone gebruiker# als root (of met sudo)

1Show the mask
```
$umask
0022
```
The RHEL default.
2Show it in letters
```
$umask -S
u=rwx,g=rx,o=rx
```
The rights that new directories get.

3Set a safer mask for this shell

$umask 027
$touch f; mkdir d; ls -ld f d
-rw-r-----. 1 student student 0 Oct 25 10:30 f
drwxr-x---. 2 student student 6 Oct 25 10:30 d

Others get nothing.

4Make it permanent for one user
```
$echo "umask 027" >> ~/.bashrc
```
Valid from the next shell.
5Make it permanent for all users
```
#echo "umask 027" > /etc/profile.d/umask.sh
```
Read at every login shell.
6Very private files
```
$umask 077
```
Files 600, folders 700.
7Set the umask with letters
```
$umask u=rwx,g=rx,o=
$umask
0027
```
Same as 027.
8Use a mask for one command only
```
$(umask 077; openssl genrsa -out private.key 4096)
```
The key file is private from the start (no time window).
9Set the umask of a service
```
#systemctl edit myapp
```
Add [Service] and UMask=0027 — shell files do not affect services.
10Check the default of new users
```
$grep -E '^(UMASK|HOME_MODE)' /etc/login.defs
UMASK		022
HOME_MODE	0700
```
login.defs sets the umask for login and the mode of new home folders.
11Why a file never gets x from the umask
```
$umask 000; touch x; ls -l x
-rw-rw-rw-. 1 student student 0 Oct 25 10:35 x
```
Files start at 666; add x with chmod.

Let op

The umask is not a chmod: it only affects files created later.
A default ACL on a directory replaces the umask for new files in it.

Bestanden

~/.bashrc: umask for one user.
/etc/profile.d/*.sh: umask for all login shells.
/etc/login.defs: UMASK and HOME_MODE.

`umask`

Wat het doet

Zo schrijf je het

Opties 3

Voorbeelden 11

1Show the mask

2Show it in letters

3Set a safer mask for this shell

4Make it permanent for one user

5Make it permanent for all users

6Very private files

7Set the umask with letters

8Use a mask for one command only

9Set the umask of a service

10Check the default of new users

11Why a file never gets x from the umask

Let op

Bestanden

Volledige handleiding

Wat het doet

Zo schrijf je het

Opties 3

Voorbeelden 11

1Show the mask

2Show it in letters

3Set a safer mask for this shell

4Make it permanent for one user

5Make it permanent for all users

6Very private files

7Set the umask with letters

8Use a mask for one command only

9Set the umask of a service

10Check the default of new users

11Why a file never gets x from the umask

Let op

Bestanden

Verwante commando's

Gebruikt in deze lessen

Volledige handleiding

`umask`