hidepid is used to prevent users from seeing all processes that do not belong to them, but it doesn't offer the possibility of selecting a specific process. Is it possible to hide only one process on a Linux machine?
A bit dirty, and there is probably a cleaner solution (maybe using SELinux or grsec), but you can hide a process by mounting an empty directory inside of
For example, something like this:
mount -o bind /empty/dir /proc/42
will prevent regular users from seeing process 42.
They will, however, see that something is hidden as they will be able to see the mount point.
If you want to do this for a service you would have to do this every time it is started, using its init script or whatever.
If you want to hide the pid only from a specific user, you could play with namespaces (maybe using
pam_namespace) to have the mount bind done only in the namespace of the target user.
In order to reverse this, simply run:
Since kernel 3.3 it has implemented something to make what you need.
hidepid=n (since Linux 3.3) This option controls who can access the information in /proc/[pid] directories. The argument, n, is one of the following values: 0 Everybody may access all /proc/[pid] directories. This is the traditional be‐ havior, and the default if this mount option is not specified. 1 Users may not access files and subdirectories inside any /proc/[pid] directo‐ ries but their own (the /proc/[pid] directories themselves remain visible). Sensitive files such as /proc/[pid]/cmdline and /proc/[pid]/status are now protected against other users. This makes it impossible to learn whether any user is running a specific program (so long as the program doesn't otherwise reveal itself by its behavior). 2 As for mode 1, but in addition the /proc/[pid] directories belonging to other users become invisible. This means that /proc/[pid] entries can no longer be used to discover the PIDs on the system. This doesn't hide the fact that a process with a specific PID value exists (it can be learned by other means, for example, by "kill -0 $PID"), but it hides a process's UID and GID, which could otherwise be learned by employing stat(2) on a /proc/[pid] directory. This greatly complicates an attacker's task of gathering information about running processes (e.g., discovering whether some daemon is running with ele‐ vated privileges, whether another user is running some sensitive program, whether other users are running any program at all, and so on). gid=gid (since Linux 3.3) Specifies the ID of a group whose members are authorized to learn process informa‐ tion otherwise prohibited by hidepid (i.e., users in this group behave as though /proc was mounted with hidepid=0). This group should be used instead of ap‐ proaches such as putting nonroot users into the sudoers(5) file.
That's useful because you can choose who can read /proc/PID.
So in case you want to try it remember to remount /proc according your needs:
: su - Password: root@foo:~# mount -o remount,hidepid=2 /proc root@foo:~# exit logout :ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND tntx 709 0.0 0.1 33980 8012 tty2 S 18:12 0:00 irssi tntx 746 0.0 0.0 8868 3880 tty1 S 18:13 0:00 -ksh93
So now I have no way to see other process than mine via PS(1) or lsof(8)