One of the more interesting aspects of certain flavors of UN*X (Linux among them) is the /proc filesystem. This « virtual » filesystem has several key features which are interesting, useful and helpful. It can also be dangerous and disastrous. This column will approach the /proc filesystem in three areas:
- A brief explanation of what it is
- What
/proccan be used for (or sometimes not to be used for) - A map of
/procas of the 2.2 Kernel on the i686 architecture
What is /proc?
Table des matières
The /proc filesystem is a direct reflection of the system kept in memory and represented in a hierarchal manner. The effort of the /proc filesystem is to provide an easy way to view kernel and information about currently running processes. As a result, some commands (ps for example) read /proc directly to get information about the state of the system. The premise behind /proc is to provide such information in a readable manner instead of having to invoke difficult to understand system calls.
What /proc can do for an Administrator
The /proc fs can be used for system related tasks such as:
- Viewing Statistical Information
- Finding out Hardware Information
- Modifying Runtime Parameters
- Viewing and Modifying Network and Host Parameters
- Memory and Performance Information
There are some things to take note of, most of those tasks can be done with tools that either peruse /proc or query the kernel directly.
Different Kernels = Different Capabilities
Different kernels can allow for different changes and information that is presented within /proc. Some, all, or totally different layouts and capabilities may exist depending on your machine’s kernel implementation.
The Obligatory Warning
Since there is no one place that documents exactly what you can and cannot do with /proc (again because of distro’s) there is no fool-proofing it other than only root may actually descend /proc and monkey with the files therein. I have found the easiest approach to be a sort of hacker method – backup your kernel and apply common sense when making alterations within the /proc fs.
A prime example of tuning applications via /proc can be found at the The C10k problem document at Dan Kegel’s Web Hostel.
A Map of /proc
Following is a table with brief descriptions of files and directories in /proc with the 2.2 kernel on a Linux i686 architecture.
loadavg |
Average of system load for the last 1, 5 and 15 minutes |
uptime |
Time in seconds since boot-up and total time used by processes |
meminfo |
The number of total, used and free bytes of memory and swap area(s) |
kmsg |
Kernel messages that have yet to be read in by the kernel |
version |
Current rev of the kernel and/or distribution (read from linux_banner |
cpuinfo |
Recognized processor parameters |
pci |
Current occupation of pci slots. |
self/ |
Information about processes currently accessing /proc |
net/ |
Descriptions about the network layer(s) |
scsi/ |
Contains files with information on individual scsi devices |
malloc |
Monitoring provisions for kmalloc and kfree operations |
kcore |
A core dump for the kernel (memory snapshot) |
modules |
Information regarding single loaded modules |
stat |
General Linux Statistics |
devices |
Information about kernel registered devices on the system |
interrupts |
Interrupt assignment information |
filesystems |
Existing filesystem implementations |
ksyms |
Symbols exported by the kernel |
dma |
Occupied DMA channels |
ioports |
Currently occupied IO ports |
smp |
Individual information about CPU’s if SMP is enabled |
cmdline |
Command line parameters passed to the kernel at boot time |
sys/ |
Important kernel and network information |
mtab |
Currently mounted filesystems |
md |
Multiple device driver information (if enabled) |
rc |
Enhanced real time clock (if enabled) |
locks |
Currently locked files |
Numbered Directories
The number directories are running process information by PID.
Results May Vary
Again, keep in mind that the capabilities of /proc and it’s contents do vary version to version, otherwise, happy exploring.
For More Information
Below is a short list of sites with in depth information (LDP aside of course) about /proc contributed by readers:
- The /proc File System
- The C10k problem
Copyright © 1999, Jay Fink
Published in Issue 46 of Linux Gazette, October 1999
