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PROCFS(4) Device Drivers Manual PROCFS(4)

procfs — process file system

proc		/proc	procfs	rw 0 0

This functionality is deprecated. Users are advised to use libprocstat(3) and kvm(3) instead.

The process file system, or procfs, implements a view of the system process table inside the file system. It is normally mounted on /proc.

The procfs provides a two-level view of process space, unlike the previous FreeBSD 1.1 procfs implementation. 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 curproc which always refers to the process making the lookup request.

Each node is a directory which contains the following entries:

dbregs
The debug registers as defined by struct dbregs in <machine/reg.h>. dbregs is currently only implemented on the i386 architecture.
etype
The type of the executable referenced by the file entry.
file
A symbolic link to the file 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. If the file cannot be found, the link target is ‘unknown’.
fpregs
The floating point registers as defined by struct fpregs in <machine/reg.h>. fpregs is only implemented on machines which have distinct general purpose and floating point register sets.
map
A collection of lines describing the memory regions of the process, where each line contains the following fields:
start-address
The starting address for the region (inclusive).
end-address
The ending address for the region (exclusive).
resident
The number of resident pages.
private-resident
The number of resident pages that were private to the process.
obj
The virtual address of the struct vm_object kernel data structure describing the memory region.
access
A three character string comprising the characters ‘r’, ‘w’ and ‘x’, denoting read, write, and execute permissions respectively. The lack of a permission is represented by ‘-’.
ref_count
The number of references to the region.
shadow_count
The number of VM objects that this region is a shadow for.
flags
The flags for the object, see the flags named in <vm/vm_object.h>.
copy-on-write
Whether the region is copy-on-write. One of:
COW
A copy-on-write region.
NCOW
A non-copy-on-write region.
needs-copy
Whether the region needs a copy. One of:
NC
The region needs a copy.
NNC
The region does not need a copy.
type
The type of the region. One of:
dead
A region associated with a dead VM object.
device
A region backed by device memory.
none
A region not backed by anything.
phys
A region backed by physical memory.
swap
A region backed by swap.
unknown
A region of unknown type.
vnode
A region backed by a file.
fullpath
The path to the file backing the memory region, or ‘-’ if there is no such file.
cred
One of:
CH
The region is being charged to the user specified in the ‘charged-uid’ field.
NCH
The region is not being charged to any user.
charged-uid
The UID of the user being charged, or -1 if no user is being charged.
mem
The complete virtual memory image of the process. Only those address 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.
note
Used for sending signals to the process. Not implemented.
notepg
Used for sending signal to the process group. Not implemented.
osrel
Allows read and write of the kernel osrel value assigned to the process. It affects the compatibility shims that are turned on and off depending on the value. Initial process value is read from the ABI note tag in the executed ELF image, and is zero if the tag not supported by binary format or was not found.
regs
Allows read and write access to the process' register set. This file contains a binary data structure struct regs defined in <machine/reg.h>. regs can only be written when the process is stopped.
rlimit
This is a read-only file containing the process current and maximum limits. Each line is of the format rlimit current max, with -1 indicating infinity.
status
The process status. This file is read-only and returns a single line containing multiple space-separated fields as follows:

  • command name
  • process id
  • parent process id
  • process group id
  • session id
  • device name of the controlling terminal, or a minus sign (“-”) if there is no controlling terminal.
  • a list of process flags: ctty if there is a controlling terminal, sldr if the process is a session leader, noflags if neither of the other two flags are set.
  • the process start time in seconds and microseconds, comma separated.
  • the user time in seconds and microseconds, comma separated.
  • the system time in seconds and microseconds, comma separated.
  • the wait channel message
  • the process effective UID
  • the process real UID
  • group list, starting with the effective GID, comma-separated
  • the hostname of the jail in which the process runs, or ‘-’ to indicate that the process is not running within a jail.

Each node is owned by the process's user, and belongs to that user's primary group.

/proc
normal mount point for the procfs.
/proc/pid
directory containing process information for process pid.
/proc/curproc
directory containing process information for the current process
/proc/self
directory containing process information for the current process
/proc/curproc/cmdline
the process executable name
/proc/curproc/etype
executable type
/proc/curproc/exe
executable image
/proc/curproc/file
executable image
/proc/curproc/fpregs
the process floating point register set
/proc/curproc/map
virtual memory map of the process
/proc/curproc/mem
the complete virtual address space of the process
/proc/curproc/note
used for signaling the process
/proc/curproc/notepg
used for signaling the process group
/proc/curproc/osrel
the process osrel value
/proc/curproc/regs
the process register set
/proc/curproc/rlimit
the process current and maximum rlimit
/proc/curproc/status
the process' current status

To mount a procfs file system on /proc:

mount -t procfs proc /proc

procstat(1), mount(2), sigaction(2), unmount(2), kvm(3), libprocstat(3), pseudofs(9)

This manual page written by Garrett Wollman, based on the description provided by Jan-Simon Pendry, and revamped later by Mike Pritchard.

June 23, 2024 dev