By default the umask is 0022:
usera@cmp$ touch somefile; ls -l total 0 -rw-r--r-- 1 usera usera 0 2009-09-22 22:30 somefile
/home/shared/ is meant for shared files and should be owned by
root and the
shared group. Files created here by
usern (any user) are automatically owned by the
shared group. There is a cron-job taking care of changing owning user and owning group (of any moved files) once per day:
usera@cmp$ cat /etc/cron.daily/sharedscript #!/bin/bash chown -R root:shared /home/shared/ chmod -R 770 /home/shared/
I was writing a really large file to the shared directory. It had me (
usera) as owning user and the
shared group as group owner. During the write operation the cron job was run, and I still had no problem completing the write process.
You see. I thought this would happen:
- I am writing the file. The file permissions and ownership data for the file looks like this:
-rw-r--r-- usera shared
- The cron job kicks in! The chown line is processed and now the file is owned by the
rootuser and the
- As the owning group only has read access to the file I get a file write error! Boom! End of story.
Why did the operation succeed? A link to some kind of reference documentation to back up the reason would be very welcome (as I could use it to study more details).