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.
News
-
Gnome 47.1 Released with a Few Fixes
The latest release of the Gnome desktop is all about fixing a few nagging issues and not about bringing new features into the mix.
-
System76 Unveils an Ampere-Powered Thelio Desktop
If you're looking for a new desktop system for developing autonomous driving and software-defined vehicle solutions. System76 has you covered.
-
VirtualBox 7.1.4 Includes Initial Support for Linux kernel 6.12
The latest version of VirtualBox has arrived and it not only adds initial support for kernel 6.12 but another feature that will make using the virtual machine tool much easier.
-
New Slimbook EVO with Raw AMD Ryzen Power
If you're looking for serious power in a 14" ultrabook that is powered by Linux, Slimbook has just the thing for you.
-
The Gnome Foundation Struggling to Stay Afloat
The foundation behind the Gnome desktop environment is having to go through some serious belt-tightening due to continued financial problems.
-
Thousands of Linux Servers Infected with Stealth Malware Since 2021
Perfctl is capable of remaining undetected, which makes it dangerous and hard to mitigate.
-
Halcyon Creates Anti-Ransomware Protection for Linux
As more Linux systems are targeted by ransomware, Halcyon is stepping up its protection.
-
Valve and Arch Linux Announce Collaboration
Valve and Arch have come together for two projects that will have a serious impact on the Linux distribution.
-
Hacker Successfully Runs Linux on a CPU from the Early ‘70s
From the office of "Look what I can do," Dmitry Grinberg was able to get Linux running on a processor that was created in 1971.
-
OSI and LPI Form Strategic Alliance
With a goal of strengthening Linux and open source communities, this new alliance aims to nurture the growth of more highly skilled professionals.