I don't understand what is owner of process. Owner of bash is me. Then who is owner of init and xterm? I searched on google but I can't find.

  • How about taking a look and see for yourself? ( ps, top, etc )
    – psusi
    Dec 10 '13 at 3:10

Processes normally have a user and group id they run at, processes that are started with root permission (user id 0), can change the id they are running with (e.g. your webserver can run as user www-data).

During startup initial user id is 0, for something that is started by a logged in user it is (in most cases) the id of the user.

So you do not really own those processes, they run with your id, and that allows you to kill them etc. The ids of a process also determine what directories can be accessed and which files changed/created.


Processes have lineages just like people. So in the same way people have parents, so do processes. If you look at the output of ps you can see who owns a particular process.

$ ps -eaf | head -10
root         1     0  0 Dec07 ?        00:00:07 /usr/lib/systemd/systemd --system --deserialize 24
root         2     0  0 Dec07 ?        00:00:00 [kthreadd]
root         3     2  0 Dec07 ?        00:00:03 [ksoftirqd/0]
root         5     2  0 Dec07 ?        00:00:00 [kworker/0:0H]
root         7     2  0 Dec07 ?        00:00:00 [kworker/u:0H]
root         8     2  0 Dec07 ?        00:00:06 [migration/0]
root         9     2  0 Dec07 ?        00:00:00 [rcu_bh]
root        10     2  0 Dec07 ?        00:00:56 [rcu_sched]
root        11     2  0 Dec07 ?        00:00:00 [watchdog/0]

The 1st column is the user that owns the process. The 2nd column is the process ID (PID) assigned to that process. And the 3rd column is the parent process ID (PPID). This PPID is what chains a process to a previous process, so in effect the PPID is the parent process ID for a particular process.

These are examples of processes that are other users (besides root) that have PPID's of processes owned by user root.


Owned by user avahi:

avahi      511     1  0 Dec07 ?        00:00:00 avahi-daemon: running [greeneggs.local]

Owned by user dbus:

dbus       512     1  0 Dec07 ?        00:00:22 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation

Here we can see where a process started by a process owned by root eventually spans a process owned by my username saml.

root      1266   547  0 Dec07 ?        00:00:00 gdm-session-worker [pam/gdm-password]
saml      1277  1266  0 Dec07 ?        00:00:03 gnome-session

Notice that gnome-session's PPID is 1277.

Lastly you can use slightly different switches to ps to see a visual tree of lineage.

$ ps -auxf
root       530  0.0  0.0 296804  1824 ?        Ssl  Dec07   0:00 /usr/sbin/gdm
root       547  0.0  0.0 380436  2208 ?        Sl   Dec07   0:00  \_ /usr/libexec/gdm-simple-slave --display-id /org/gnome/Dis
root       584  4.0  0.5 297980 40816 tty1     Ss+  Dec07  86:37      \_ /usr/bin/Xorg :0 -background none -verbose -auth /run
root      1266  0.0  0.0 516956  3160 ?        Sl   Dec07   0:00      \_ gdm-session-worker [pam/gdm-password]
saml      1277  0.0  0.0 714828  6336 ?        Ssl  Dec07   0:03          \_ gnome-session

Each process runs as a particular user. (It's called “user”, not “owner”.) The user determines the processes's rights. In particular, if a process is running as the user sumi, then whenever that process tries to access a file, the “user” permissions on that file apply (first rwx group of the ls -l output, first digit of the octal mode).

A number of things are restricted to processes running as the same user, such as sending signals (killing) and obtaining debugging information.

All the processes that you interact with directly — shell, terminal emulator, browser, etc. — run as your user.

The user that a process is running as is unrelated to the user who owns the disk file containing the program. Most programs are installed system-wide and owned by root, but when the program is executed, the process runs as the user who started it.

The init process, like other core system processes, runs as the system user, root. The root user has more rights than other users.

(This is to get you started. I've simplified several aspects of process users, privileges and file access rights.)

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