Linux file permissions (Dateirechte)


                                            Everything is a file !

[admin123@debian11 file_permissions]$ ls
directory1 file1

[admin123@debian11 file_permissions]$ ls -l
insgesamt 4
drwxr-xr-x    2 admin123 admin123 4096  4. Jun 10:19 directory1
-rw-rw-r--     1 admin123 admin123       0  4. Jun 09:44 file1


[admin123@debian11 file_permissions]$ ls -la
insgesamt 12
drwxr-xr-x     8  admin123 admin123 4096   5. Jun 09:41  .                    <- this is a file
drwxr-xr-x     4  root           root          4096 20. Apr 13:43 ..                   <- this is a file
drwxr-xr-x     2  admin123 admin123 4096   4. Jun 10:19 directory1     <- this is a file
-rw-r--r--       1  admin123 admin123       0    4. Jun 09:44 file1              <- this is a file

     |                 |         |                 |          |          |                 |
     |                 |         |                 |          |          |                 file
     |                 |         |                 |          |          date and time
     |                 |         |                 |          size
     |                 |         |                group, who owns the file
     |                 |         user, who owns the file
     |                 hard links to a file
    file permissions


file and directory permissions
files have permissions and directories have permissions.

X-rwx-rwx-rwx
 |     |       |       |
 |     |       |       others permissions
 |     |       group permisions
 |     owner permissions
 filetype: d=directory, l=link,
 
read      (r)     =>   100   =>   4
write     (w)   =>   010   =>   2
execute (x)    =>   001   =>   1

421    ---        read, write, execute

0        ---        no permission
1        --x       execute
2        -w-      write
3        -wx     write and execute
4        r--        read
5        r-x       read and execute
6        rw-      read and write
7        rwx     read, write and execute


umask
For a new file the umask is subtracted from 0777 for directories
and 0666 from files.

The default mask for non-root users is 002,
the default mask for root is 022.

new files for non-root: 0664 (0666 - 002)
new directories for non-root: 0775 (0777 - 002)

new files for root: 0644 (0666 - 022)
new directories for root: 0775 (0777 - 022)

SUID = Setuid = user id bit    =  rws rwx rwx
SGID = Setgid = group id bit =  rwx rws rwx
Sticky Bit                                =  rwx rwx rwt

commands
ls         -  list directory contents                   man ls
chmod - change file mode bits                    man chmod
chown - change file owner an group           man chown
chgrp  -  change group ownership               man chgrp
touch  -  create file or change timestamps   man touch


changing permissions:
chmod:
chmod u=rwx,g=rx,o=rx  <file> ≙  chmod 755 <file>  ≙  chmod u+rwx,g+rx,o+rx <file>