Default Permissions and umask

The umask on Photon OS is set to 0027.

When you create a new file with the touch command as root, the default on Photon OS is to set the permissions to 0640--which translates to read-write for user, read for group, and no access for others. Here's an example:

touch newfile.md
stat newfile.md
  File: 'newfile.md'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 801h/2049d      Inode: 316454      Links: 1
Access: (0640/-rw-r-----)  Uid: (    0/    root)   Gid: (    0/    root)

When you create a directory as root, Photon OS sets the permissions to 0750:

mkdir newdir
stat newdir
  File: 'newdir'
  Size: 4096            Blocks: 8          IO Block: 4096   directory
Device: 801h/2049d      Inode: 316455      Links: 2
Access: (0750/drwxr-x---)  Uid: (    0/    root)   Gid: (    0/    root)

Because the mkdir command uses the umask to modify the permissions placed on newly created files or directories, you can see umask at work in the permissions of the new directory. Its default permissions are set at 0750 after the umask subtracts 0027 from the full set of open permissions, 0777.

Similarly, a new file begins as 0666 if you were to set umask to 0000. But because umask is set by default to 0027, a new file's permissions are set to 0640.

So be aware of the default permissions on the directories and files that you create. Some system services and applications might require permissions other than the default. The systemd network service, for example, requires user-defined configuration files to be set to 644, not the default of 640. Thus, after you create a network configuration file with a .network extension, you must run the chmod command to set the new file's mode bits to 644. For example:

chmod 644 10-static-en.network 

For more information on permissions, see the man pages for stat, umask, and acl.