/proc is not a real file system, it is a virtual file system. For example, if you do ls -l /proc/stat, you’ll notice that it has a size of 0 bytes, but if you do “cat /proc/stat”, you’ll see some content inside the file.
Several Linux commands access the information from /proc, and displays in a certain format.
1. /proc Directories with names as numbers
Do a ls -l /proc, and you’ll see lot of directories with just numbers. These numbers represents the process ids, the files inside this numbered directory corresponds to the process with that particular PID.
Following are the important files located under each numbered directory (for each process):
- cmdline – command line of the command.
- environ – environment variables.
- fd – Contains the file descriptors which is linked to the appropriate files.
- limits – Contains the information about the specific limits to the process.
- mounts – mount related information
Following are the important links under each numbered directory (for each process):
- cwd – Link to current working directory of the process.
- exe – Link to executable of the process.
- root – Link to the root directory of the process.
2. /proc Files about the system information
Following are some files which are available under /proc, that contains system information such as cpuinfo, meminfo, loadavg.
- /proc/cpuinfo – information about CPU,
- /proc/meminfo – information about memory,
- /proc/loadvg – load average,
- /proc/partitions – partition related information,
- /proc/version – linux version
Some Linux commands read the information from this /proc files and displays it. For example, free command, reads the memory information from /proc/meminfo file, formats it, and displays it.
To learn more about the individual /proc files, do “man 5 FILENAME”.
- /proc/cmdline – Kernel command line
- /proc/cpuinfo – Information about the processors.
- /proc/devices – List of device drivers configured into the currently running kernel.
- /proc/dma – Shows which DMA channels are being used at the moment.
- /proc/fb – Frame Buffer devices.
- /proc/filesystems – File systems supported by the kernel.
- /proc/interrupts – Number of interrupts per IRQ on architecture.
- /proc/iomem – This file shows the current map of the system’s memory for its various devices
- /proc/ioports – provides a list of currently registered port regions used for input or output communication with a device
- /proc/loadavg – Contains load average of the system
The first three columns measure CPU utilization of the last 1, 5, and 10 minute periods.
The fourth column shows the number of currently running processes and the total number of processes.
The last column displays the last process ID used.
- /proc/locks – Displays the files currently locked by the kernel
1: POSIX ADVISORY WRITE 14375 08:03:114727 0 EOF
- /proc/meminfo – Current utilization of primary memory on the system
- /proc/misc – This file lists miscellaneous drivers registered on the miscellaneous major device, which is number 10
- /proc/modules – Displays a list of all modules that have been loaded by the system
- /proc/mounts – This file provides a quick list of all mounts in use by the system
- /proc/partitions – Very detailed information on the various partitions currently available to the system
- /proc/pci – Full listing of every PCI device on your system
- /proc/stat – Keeps track of a variety of different statistics about the system since it was last restarted
- /proc/swap – Measures swap space and its utilization
- /proc/uptime – Contains information about uptime of the system
- /proc/version – Version of the Linux kernel, gcc, name of the Linux flavor installed.