How to deny other people to see my running details after “top” command and press key “c”

Question

In my school, we share one server to run programs.

Using top we can see the situation of the server, if press key c, we even can see the command details, somehow including my lab data information.

So how can I deny other people to see my running details even after using c? Can it only show the name of the process, java or awk, but hide the details.

Answer 1

Hiding your user info

So with top its default behavior is to show all the processes on the box and you can't really deny other users from seeing these details. Methods for doing this are discussed in this U&L Q&A titled:

• How to make a process invisible to other users?
• Hiding Linux Processes For Fun And Profit
• Is it possible to 'hide' a process from the listing of ps or top on Linux

The 3rd link shows an interesting method which is a kernel patch that added an option called hidepid to mount in Linux kernels 3.3+:

$ mount /proc -o remount,hidepid=2

hidepid=0 (default) means the old behavior - anybody may read all world-readable /proc/PID/* files.

hidepid=1 means users may not access any /proc// directories, but their own. Sensitive files like cmdline, sched*, status are now protected against other users. As permission checking done in proc_pid_permission() and files' permissions are left untouched, programs expecting specific files' modes are not confused.

hidepid=2 means hidepid=1 plus all /proc/PID/ will be invisible to other users. It doesn't mean that it hides whether a process exists (it can be learned by other means, e.g. by kill -0 $PID), but it hides process' euid and egid. It compicates intruder's task of gathering info about running processes, whether some daemon runs with elevated privileges, whether another user runs some sensitive program, whether other users run any program at all, etc.

gid=XXX defines a group that will be able to gather all processes' info (as in hidepid=0 mode). This group should be used instead of putting nonroot user in sudoers file or something. However, untrusted users (like daemons, etc.) which are not supposed to monitor the tasks in the whole system should not be added to the group.

NOTE: This doesn't give you any ability to control visibility, only restrict users to see their details under /proc.

Hiding other user's info

If you want to hide other users when you're using top you can do that like this:

$ top -u '!root'
...
top - 00:04:16 up 2 days,  1:51,  1 user,  load average: 0.00, 0.01, 0.05
Tasks:  80 total,   1 running,  79 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.3 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  1016156 total,   204212 free,    80104 used,   731840 buff/cache
KiB Swap:  2097148 total,  2097148 free,        0 used.   755224 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
  597 dbus      20   0   26668   1924   1364 S  0.0  0.2   0:08.55 dbus-daemon
  633 polkitd   20   0  536264  10216   4796 S  0.0  1.0   0:00.35 polkitd
  634 libstor+  20   0    8576    816    668 S  0.0  0.1   0:00.49 lsmd
 1305 postfix   20   0   91956   4292   3232 S  0.0  0.4   0:00.09 qmgr
 4199 vagrant   20   0  152392   3020   1424 S  0.0  0.3   0:01.53 sshd
 4200 vagrant   20   0  116196   2928   1796 S  0.0  0.3   0:00.05 bash
 5622 postfix   20   0   91776   4044   3028 S  0.0  0.4   0:00.00 pickup
 5672 user1     20   0  116096   2864   1808 S  0.0  0.3   0:00.04 bash
 5758 user1     20   0  157624   2136   1544 R  0.0  0.2   0:00.00 top

The notation, '!root' means to not show the root user.