O'Reilly logo

Shell Scripting: Expert Recipes for Linux, Bash, and More by Steve Parker

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Other Features of /proc and /sys

As mentioned previously, the /proc filesystem on Linux exposes a lot of detail about the kernel, which is not (as it may first seem) a static set of files created at boot, but is a direct hook into the kernel itself. Accordingly, some files can be written to, some can be read, and others can be read or written. A number of features in /proc are described in the proc(5) man page; run man 5 proc to read it. These files can be very useful for shell scripts because a shell script can get very close to the internals of the kernel itself, which is unusual for a Unix-like system.

Version

/proc/version is a read-only listing of the kernel version, including build details of how it was compiled. This can be a more complete, and more accurate, way to detect the actual kernel version than uname. Despite how it looks here, it is actually a single line of text.

cat /proc/version
Linux version 2.6.32-5-amd64 (Debian 2.6.32-29) (ben@decadent.org.uk) (gcc version
 4.3.5 (Debian 4.3.5-4) ) #1 SMP Fri Dec 10 15:35:08 UTC 2010
$ uname -a
Linux goldie 2.6.32-5-amd64 #1 SMP Fri Dec 10 15:35:08 UTC 2010 x86_64 GNU/Linux
$

SysRq

There is a little-used key on the PC keyboard, labeled SysRq. Its history goes back to mainframe computer systems, but it is used by the Linux kernel as a way to communicate with the kernel even when normal methods (such as echoing to /proc as most of these examples cover) are not possible. If enabled, when the user presses the “magic” combination ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required