.\" Written by Garrett Wollman
.\" This file is in the public domain.
.\"
.Dd May 29, 2025
.Dt LINPROCFS 4
.Os
.Sh NAME
.Nm linprocfs
.Nd Linux process file system
.Sh SYNOPSIS
.Bd -literal
linproc		/compat/linux/proc	linprocfs	rw 0 0
.Ed
.Sh DESCRIPTION
The Linux process file system, or
.Nm ,
emulates a subset of Linux' process file system and is required for
the complete operation of some Linux binaries.
.Pp
The
.Nm
provides a two-level view of process space.
At the highest level, processes themselves are named, according to
their process ids in decimal, with no leading zeros.
There is also a special node called
.Pa self
which always refers to the process making the lookup request.
.Pp
Each process node is a directory containing several files:
.Bl -tag -width oom_score_adj
.It Pa auxv
The auxiliary vector passed to the program.
.It Pa cmdline
The command line used to execute the process.
.It Pa cwd
A symbolic link pointing to the current work directory of the process.
.It Pa environ
The list of environment variables and values of the process.
Every variable and pair value is separated from the next by a NULL byte.
.It Pa exe
A reference to the vnode from which the process text was read.
This can be used to gain access to the process' symbol table,
or to start another copy of the process.
.It Pa limits
The soft and hard limits for the process along with the units used.
.It Pa maps
Memory map of the process.
.It Pa mem
The complete virtual memory image of the process.
Only those addresses which exist in the process can be accessed.
Reads and writes to this file modify the process.
Writes to the text segment remain private to the process.
.It Pa mountinfo
Information about mount points.
.It Pa mounts
Similar to the above.
.It Pa oom_score_adj
Score adjustment for the Out Of Memory killer.
.It Pa root
Symbolic link to the root directory for this process.
.It Pa stat
Process statistics.
It includes user, nice, system, idle, iowait, irq, softirq,
steal, guest and guest_nice.
.It Pa statm
Process size statistics.
It includes total program size, resident set size, number of resident shared
pages (unused), text size, library size (unused), data + stack and dirty pages
(unused).
.It Pa status
Process statistics in human readable form.
It includes process name, state, PID,
etc.
.It Pa task
Dummy directory to avoid problems in specific software such as Chromium.
.El
.Pp
Each node is owned by the process's user, and belongs to that user's
primary group, except for the
.Pa mem
node, which belongs to the
.Li kmem
group.
.Sh FILES
.Bl -tag -width /compat/linux/proc/filesystems -compact
.It Pa /compat/linux/proc
The normal mount point for
.Nm .
.It Pa /compat/linux/proc/cmdline
Contains the path of the kernel image used to boot the system.
.It Pa /compat/linux/proc/cpuinfo
CPU vendor and model information in human-readable form.
.It Pa /compat/linux/proc/devices
List of character and block devices.
The later is usually empty on
.Fx .
.It Pa /compat/linux/proc/filesystems
List of supported filesystems.
For pseudo filesystems, the first column contains
.Em nodev .
.It Pa /compat/linux/proc/meminfo
System memory information in human-readable form.
.It Pa /compat/linux/proc/modules
Loaded kernel modules.
Empty for now.
.It Pa /compat/linux/proc/mounts
Devices corresponding mount points.
.It Pa /compat/linux/proc/mtab
Same as above.
.It Pa /compat/linux/proc/partitions
Partition information including major and minor numbers, number of blocks and
name.
The rest of the fields are set to zero.
.It Pa /compat/linux/proc/stat
System statistics.
For each cpu it includes at most user time, nice time, system
time and idle time, iowait (time waiting for I/O to complete), times serving
irqs and softirq, steal, guest and guest_nice times that represent times spent
in different modes in a virtualized environment.
The last columns are set to zero.
This file also contains brief statistics for disks, context switches and
more.
.It Pa /compat/linux/proc/swap
Information about the swap device if any.
.It Pa /compat/linux/proc/uptime
Time since the last boot and time spent in idle state.
.It Pa /compat/linux/proc/version
Version of the emulated linux system.
.It Pa /compat/linux/proc/pid
A directory containing process information for process
.Pa pid .
.It Pa /compat/linux/proc/self
A directory containing process information for the current process.
.El
.Sh EXAMPLES
To mount a
.Nm
file system on
.Pa /compat/linux/proc :
.Pp
.Dl "mount -t linprocfs linproc /compat/linux/proc"
.Sh SEE ALSO
.Xr mount 2 ,
.Xr unmount 2 ,
.Xr auxv 3 ,
.Xr linux 4 ,
.Xr procfs 5 ,
.Xr pseudofs 9
.Sh HISTORY
The
.Nm
first appeared in
.Fx 4.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
was derived from
.Nm procfs
by
.An Pierre Beyssac .
This manual page was written by
.An Dag-Erling Sm\(/orgrav ,
based on the
.Xr procfs 5
manual page by
.An Garrett Wollman .