pkill in server ubuntu

Question

I used the command pkill as root on my vps ubuntu, and I got kicked out of the server and can't access it.

This is what I wrote inside the terminal:

pkill h

h is my user in ubuntu

What is the solution?

Answer 1

If you want to kill all processes belonging to a particular user, use

pkill -U user .

The . at the end matches any process name, and -U user restricts the operation to processes belonging to the user called user.

To see what processes would be affected by a pkill command, you could replace the pkill command itself with pgrep, and then possibly add -l to get "long output" (the process names would be displayed too).

pgrep -l h

The above commend should show you all commands on the system that contains the character h in its name, while the command below would show you all commands belonging to the user called user:

pgrep -l -U user .

Answer 2

You told us,

This is what I wrote inside the terminal: pkill h

Furthermore, you did this as root. What happened here is that you killed all processes containing h in the name. This included the master sshd, which controls inbound ssh requests, as well as all its children that mediate existing connections.

Unless you can log on to the non-graphical console and restart it yourself, you're going to need to arrange for your system to be forcibly rebooted.

I would strongly recommend that you get into the habit of checking the documentation for command with which you're unfamiliar. Here, man pkill shows as its very first example a method for selecting only processes owned by a particular user. Applying the example to your situation,

pkill -u h          # user "h"

Better still, use pgrep first to check you've matched the correct set of processes:

pgrep -a -u h       # -a shows "all" the command line, for user "h"

Or send signal 0, which has no action:

pkill -0 -e -u h    # Signal zero, "echo" affected processes, for user "h"

Notice that the username must be an exact match, but a process name is a partial match. (This is why h in your original command matched sshd.)