Running Linux, Third Edition

The /proc filesystem

Unix systems have come a long way with respect to providing uniform interfaces to different parts of the system; as you will learn in the next chapter, hardware is represented in Linux in the form of a special type of file. There is, however, a special filesystem called the /proc filesystem that goes even one step further: it unifies files and processes.

From the user’s or the system administrator’s point of view, the /proc filesystem looks just like any other filesystem; you can navigate around it with the cd command, list directory contents with the ls command and view file contents with the cat command. However, none of these files and directories occupy any space on your hard disk. The kernel traps accesses to the /proc filesystem and generates directory and file contents on the fly. In other words, whenever you list or directory or view file contents in the /proc filesystem, the kernel dynamically generates the contents you want to see.

To make this less abstract, let’s see some examples. The following example displays the list of files in the top-level directory of the /proc filesystem:

tigger # ls /proc 1 184 25472 8 8525 kmsg 130 185 25475 82 8526 ksyms 134 186 25497 8484 8593 loadavg 136 187 25498 8485 963 locks 139 2 25499 8488 965 meminfo 143 24924 25500 8489 9654 modules 144 25441 25515 8492 968 mounts 145 25442 25549 8496 97 net 146 25445 25550 8507 99 pci 147 25446 26019 8508 cmdline scsi 148 25449 26662 8510 cpuinfo self 151 25451 26663 8511 devices ...