MOUNT_PROCFS(8)

MOUNT_PROCFS(8) | System Manager's Manual | MOUNT_PROCFS(8)

# NAME

`mount_procfs` — mount the process file system

# SYNOPSIS

`mount_procfs` | [`-o` options] /proc mount_point

# DESCRIPTION

The `mount_procfs` command attaches an instance of the process namespace to the global filesystem namespace. The conventional mount point is /proc. The directory specified by mount_point is converted to an absolute path before use. This command is normally executed by mount(8) at boot time.

The options are as follows:

`-o` `nolinux`
  Do not support nodes which are not part of the original procfs implementation but have been added for compatibility with the Linux procfs namespace. See FILES for more information.

The root of the process filesystem contains an entry for each active process. These processes are visible as a directory whose name is the process' pid. In addition, the special entries curproc and self reference the current process. The self symlink appears for compatibility with the Linux procfs implementation.

Each directory contains several files.

cmdline
  This file is readonly and returns null-terminated strings corresponding to the process' command line arguments. For a system or zombie process, this file contains only a string with the name of the process.
cwd
  A symbolic link that points to the current working directory of the process. If the target process's current working directory is not available or is not at or below the current process's root directory, this link will point to “/”.
fd/#
  File descriptors which can be accessed through the file system. See fd(4) for more information.
file
  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.
map
  A map of the process' virtual memory. This file comprises lines describing the memory regions of the process, where each line contains the following fields:

  start-address
    The starting address of the region (inclusive).
  end-address
    The ending address of the region (exclusive).
  protection
    The access permissions for the region, represented as a three-character string using the characters ‘r’, ‘w’ and ‘x’ to denote read, write, and execute permission respectively. The lack of a permission is represented by a ‘-’.
  max-protection
    The maximum access permissions for the region represented as a three character string using the characters ‘r’, ‘w’ and ‘x’ to denote read, write, and execute permission respectively. The lack of a permission is represented by a ‘-’.
  copy-on-write
    Whether the region is copy-on-write. One of:
    COW
      A region that is copy-on-write.
    NCOW
      A region that is not copy-on-write.
  needs-copy
    Whether the region needs a copy. One of:
    NC
      The region needs a copy.
    NNC
      The region does not need a copy.
  inheritance
    The inheritance code for the region, as set by minherit(2).
  wired-count
    The wired count for the region. The region can be paged out if its wired count is zero.
  advice
    The advice value set by a prior call to madvise(2) for the region.
maps
  A map of the process' virtual memory in a form like the proc filesystem as implemented in Linux. This file comprises lines describing the memory regions of the process, where each line contains the following fields:

  start-address
    The starting address of the region (inclusive).
  end-address
    The ending address of the region (exclusive).
  protection
    The access permissions for the region, represented as a three-character string using the characters ‘r’, ‘w’ and ‘x’ to denote read, write, and execute permission respectively. The lack of a permission is represented by a ‘-’.
  copy-on-write
    Whether the region is copy-on-write. One of:
    ‘p’
      The region is copy-on-write.
    ‘s’
      The region is shared.
  offset
    The offset into the file being mapped by the region.
  device-id
    The major and minor number of the device containing the file being mapped by the region.
  fileid
    The inode for the file associated with the region.
  path
    The pathname to the file associated with the region.
mem
  The complete virtual memory image of the process. Only those addresses which exist in the process can be accessed. Writes to this file modify the process. Writes to the text segment normally remain private to the process, since the text segment is mapped with MAP_PRIVATE; however, this is not guaranteed.
note
  Not implemented.
notepg
  Not implemented.
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.
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.
root
  A symbolic link that points to the root directory of the process. If the target process's root directory is not available or is not at or below the current process's root directory, this link will point to “/”.
status
  The process status. This file is readonly and returns a single line containing multiple space-separated fields as follows:

  - command name
  - process id
  - parent process id
  - process group id
  - session id
  - major,minor of the controlling terminal, or `-1,-1` 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 credentials consisting of the effective user id and the list of groups (whose first member is the effective group id) all comma separated.

# FILES

/proc/#
/proc/#/cmdline
/proc/#/cwd
/proc/#/exe
/proc/#/file
/proc/#/fpregs
/proc/#/map
/proc/#/maps
/proc/#/mem
/proc/#/note
/proc/#/notepg
/proc/#/regs
/proc/#/root
/proc/#/status
/proc/curproc
/proc/self

If the `linux` mount option is used, the following files are also available:

/proc/#/stat
/proc/cpuinfo
/proc/devices
/proc/meminfo
/proc/mounts
/proc/uptime

# SEE ALSO

mount(2), sigaction(2), unmount(2)

# HISTORY

The `mount_procfs` utility first appeared in 4.4BSD.

# BUGS

This filesystem may not be NFS-exported since most of the functionality of `procfs` requires that state be maintained.

April 18, 2023 | NetBSD 11.0