The sys admin's daily grind: parallel SSH
Mass Start
Parallel SSH is the name of an easy-to-configure tool that our resident sys admin, Charly, now routinely deploys whenever he needs to launch the same programs, copy the same files, or kill the same processes simultaneously on multiple computers.
I am writing from a Linux seminar in the Linuxhotel in Essen, Germany. The environment here comprises four Xen virtualized machines. Identical changes to all cluster nodes are a regular requirement, which is a pain, but I have a utility up my sleeve: parallel SSH [1]. Pssh relies on the SSH agent running, so I'll take care of that first:
ssh-agent ssh-add
After I enter the pass phrase for my SSH key, the AAH agent ensures that nobody will ask me for it, at least not during the current session. Next, I need a text file in which I add the IP addresses of the servers for which I need to set up simultaneous connections, so I'll start by adding three addresses to server.txt:
192.168.5.12 192.168.5.52 192.168.5.67
First, I will open an SSH connection to these three computers, run the uname command on them, and redirect the output to my pssh-out directory with the command line:
pssh -h server.txt -l charly -o /home/charly/pssh-out uname
Now I have three files below /home/charly/pssh-out named after the server IP addresses. And lo and behold, the files contain the uname command output (Figure 1). Pssh is thus similar to the Distributed Shell (DSH).
Figure 1: Pssh launches the same example program, uname, on each machine with an entry in the server.txt list.
Two Hard-Hitting Tools
PSCP and PNuke, which are also part of the pssh package, work along the same principle.
PSCP copies files simultaneously to multiple target machines. This command adds a new message of the day to my servers:
pscp -h server.txt -l charly /etc/motd /etc/
PNuke sends a kill -9 to identically named processes on three servers
pnuke -l server.txt -l charly wget
and terminates any wget processes running on them. This frees up some bandwidth.
Conclusions
Brilliant. The most difficult thing about the pssh suite is saying its Internet page name, theether.org, without tripping over your own tongue.
Infos
- Parallel SSH: http://www.theether.org/pssh/
The Author
Charly Kühnast is a Unix operating system administrator at the Data Center in Moers, Germany. His tasks include firewall and DMZ security and availability. He divides his leisure time into hot, wet, and eastern sectors, where he enjoys cooking, fresh water aquariums, and learning Japanese, respectively.
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
US / Canada
UK / Australia
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 47.2 Now Available
Gnome 47.2 is now available for general use but don't expect much in the way of newness, as this is all about improvements and bug fixes.
-
Latest Cinnamon Desktop Releases with a Bold New Look
Just in time for the holidays, the developer of the Cinnamon desktop has shipped a new release to help spice up your eggnog with new features and a new look.
-
Armbian 24.11 Released with Expanded Hardware Support
If you've been waiting for Armbian to support OrangePi 5 Max and Radxa ROCK 5B+, the wait is over.
-
SUSE Renames Several Products for Better Name Recognition
SUSE has been a very powerful player in the European market, but it knows it must branch out to gain serious traction. Will a name change do the trick?
-
ESET Discovers New Linux Malware
WolfsBane is an all-in-one malware that has hit the Linux operating system and includes a dropper, a launcher, and a backdoor.
-
New Linux Kernel Patch Allows Forcing a CPU Mitigation
Even when CPU mitigations can consume precious CPU cycles, it might not be a bad idea to allow users to enable them, even if your machine isn't vulnerable.
-
Red Hat Enterprise Linux 9.5 Released
Notify your friends, loved ones, and colleagues that the latest version of RHEL is available with plenty of enhancements.
-
Linux Sees Massive Performance Increase from a Single Line of Code
With one line of code, Intel was able to increase the performance of the Linux kernel by 4,000 percent.
-
Fedora KDE Approved as an Official Spin
If you prefer the Plasma desktop environment and the Fedora distribution, you're in luck because there's now an official spin that is listed on the same level as the Fedora Workstation edition.
-
New Steam Client Ups the Ante for Linux
The latest release from Steam has some pretty cool tricks up its sleeve.