Process and job control
Instructions
Typing kill -l shows you the instructions that kill passes to a process. The following are the most relevant ones for your daily work:
- SIGHUP: This tells a process to restart immediately after terminating and is often used to tell servers to parse modified configuration files.
- SIGTERM: This request to terminate allows the process to clean up.
- SIGKILL: This signal forces a process to terminate come what may. But in some cases, it takes more to get rid of the process. After waiting in vain for a timeout, you have no alternative but to reboot.
- SIGSTOP: Interrupts the process until you enter SIGCONT to continue.
To send a signal to a process, you can enter either the signal name or number followed by the process ID – for example, kill -19 9201. Also, you can specify multiple process IDs. If you call kill without any parameters but with the PID, it will send the SIGTERM signal to the process.
Seek and Ye Shall Find
To find the right process ID, you can run ps as described previously. The shell command can be combined with other tools, such as grep, in the normal way. For example, you could do this (Listing 3) to find processes with ssh in their names.
Listing 3
grep ssh
Besides the SSH server (sshd), the list includes all of your SSH connections. To send the same signal to all of these processes, you would normally list the PIDs in the kill command line, which can be tricky if the list is too long.
The killall gives you a workaround – the tool understands all of the kill signals but expects process names instead of IDs.
The killall -19 ssh command sends all your SSH connections to sleep (SIGSTOP). If you do not specify the signal, killall assumes you mean SIGTERM, just like kill.
Because killall really does remove the processes in one fell swoop, it is a good idea to switch to interactive mode (-i option). For each process, the tool prompts you to decide whether to terminate.
More Detective Work
If you are looking for process IDs, a combination of ps and grep is a good idea, but you can save some typing by running pgrep instead.
To find all processes with ssh in their names, do the following:
$ pgrep ssh 2816 3992 4249
If you need more context, add the -l parameter and pgrep will reveal the names. To discover the full command line, including all arguments, combine -l and -f:
$ pgrep -lf ssh 2816 /usr/sbin/sshd 3992 ssh -X chicken@asteroid 4249 ssh chicken@nugget
« Previous 1 2 3 4 Next »
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
![Learn More](https://www.linux-magazine.com/var/linux_magazin/storage/images/media/linux-magazine-eng-us/images/misc/learn-more/834592-1-eng-US/Learn-More_medium.png)
News
-
NVIDIA Released Driver for Upcoming NVIDIA 560 GPU for Linux
Not only has NVIDIA released the driver for its upcoming CPU series, it's the first release that defaults to using open-source GPU kernel modules.
-
OpenMandriva Lx 24.07 Released
If you’re into rolling release Linux distributions, OpenMandriva ROME has a new snapshot with a new kernel.
-
Kernel 6.10 Available for General Usage
Linus Torvalds has released the 6.10 kernel and it includes significant performance increases for Intel Core hybrid systems and more.
-
TUXEDO Computers Releases InfinityBook Pro 14 Gen9 Laptop
Sporting either AMD or Intel CPUs, the TUXEDO InfinityBook Pro 14 is an extremely compact, lightweight, sturdy powerhouse.
-
Google Extends Support for Linux Kernels Used for Android
Because the LTS Linux kernel releases are so important to Android, Google has decided to extend the support period beyond that offered by the kernel development team.
-
Linux Mint 22 Stable Delayed
If you're anxious about getting your hands on the stable release of Linux Mint 22, it looks as if you're going to have to wait a bit longer.
-
Nitrux 3.5.1 Available for Install
The latest version of the immutable, systemd-free distribution includes an updated kernel and NVIDIA driver.
-
Debian 12.6 Released with Plenty of Bug Fixes and Updates
The sixth update to Debian "Bookworm" is all about security mitigations and making adjustments for some "serious problems."
-
Canonical Offers 12-Year LTS for Open Source Docker Images
Canonical is expanding its LTS offering to reach beyond the DEB packages with a new distro-less Docker image.
-
Plasma Desktop 6.1 Released with Several Enhancements
If you're a fan of Plasma Desktop, you should be excited about this new point release.