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Chapter 2. The /proc File System 37

2.2.29. /proc/uptime

This ﬁle contains information about how long the system has on since its last restart. The output of

/proc/uptime is quite minimal:

350735.47 234388.90

The ﬁrst number tells you the total number of seconds the system has been up. The second number

tells you how much of that time, also in seconds, the machine has spent idle.

2.2.30. /proc/version

This ﬁles tells you the versions of the Linux kernel and gcc, as well as the version of Red Hat Linux

installed on the system:

Linux version 2.4.18-0.4 ([email protected]) (gcc version 2.96 20000731

(Red Hat Linux 7.2 2.96-106)) #1 Wed Mar 13 10:47:08 EST 2002

This information is used for a variety of purposes, including the version data presented when a user

logs in.

2.3. Directories in /proc

Common groups of information concerning the kernel are grouped into directories and subdirectories

within the /proc directory.

2.3.1. Process Directories

Every /proc directory contains a number of directories numerical names. A listing of them starts off

like this:

dr-xr-xr-x 3 root root 0 Feb 13 01:28 1

dr-xr-xr-x 3 root root 0 Feb 13 01:28 1010

dr-xr-xr-x 3 xfs xfs 0 Feb 13 01:28 1087

dr-xr-xr-x 3 daemon daemon 0 Feb 13 01:28 1123

dr-xr-xr-x 3 root root 0 Feb 13 01:28 11307

dr-xr-xr-x 3 apache apache 0 Feb 13 01:28 13660

dr-xr-xr-x 3 rpc rpc 0 Feb 13 01:28 637

dr-xr-xr-x 3 rpcuser rpcuser 0 Feb 13 01:28 666

These directories are called process directories, as they are named after a program’s process ID and

contain information speciﬁc to that process. The owner and group of each process directory is set to

the user running the process. When the process is terminated, its /proc process directory vanishes.

However, while the process is running, a great deal of information speciﬁc to that process is held

within its directory.

Each of the process directories contains the following ﬁles:

• cmdline — Contains the command line arguments that started the process. The output of cmdline

ﬁle for the sshd process looks like this:

/usr/sbin/sshd

• cpu — Provides speciﬁc information about the utilization of each of the system’s CPUs. A process

running on a dual CPU system produces output similar to this:

cpu 11 3

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 ... 281 282

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 37