.\"	$OpenBSD: mount_procfs.8,v 1.21 2003/06/03 13:16:08 jmc Exp $
.\"	$NetBSD: mount_procfs.8,v 1.6 1995/03/18 14:58:10 cgd Exp $
.\"
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.\"	@(#)mount_procfs.8	8.2 (Berkeley) 3/27/94
.\"
.Dd March 27, 1994
.Dt MOUNT_PROCFS 8
.Os
.Sh NAME
.Nm mount_procfs
.Nd mount the process file system
.Sh SYNOPSIS
.Nm mount_procfs
.Op Fl o Ar options
.Pa /proc
.Pa mount_point
.Sh DESCRIPTION
The
.Nm
command attaches an instance of the process
namespace to the global filesystem namespace.
The conventional mount point is
.Pa /proc .
This command is normally executed by
.Xr mount 8
at boot time.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl o Ar options
Options are specified with a
.Fl o
flag followed by a comma separated string of options.
See the
.Xr mount 8
man page for possible options and their meanings.
The following procfs specific option is also available:
.Bl -tag -width indent
.It linux
Add Linux compatibility links and nodes to procfs.
.El
.El
.Pp
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's PID.
In addition, the special entry
.Pa curproc
references the current process.
.Pp
Each directory contains several files.
.Bl -tag -width status
.It Pa ctl
A write-only file which supports a variety
of control operations.
Control commands are written as strings to the
.Pa ctl
file.
The control commands are:
.Pp
.Bl -tag -width detach -compact
.It attach
Stops the target process and arranges for the sending
process to become the debug control process.
.It detach
Continues execution of the target process and
removes it from control by the debug process (which
need not be the sending process).
.It run
Continues running the target process until
a signal is delivered, a breakpoint is hit, or the
target process exits.
.It step
Single steps the target process, with no signal delivery.
.It wait
Waits for the target process to come to a steady
state ready for debugging.
The target process must be in this state before
any of the other commands are allowed.
.El
.Pp
The string can also be the name of a signal, lower case
and without the
.Dv SIG
prefix,
in which case that signal is delivered to the process
(see
.Xr sigaction 2 ) .
.It Pa file
A reference to the vnode from which the process text was read.
This can be used to gain access to the process's symbol table,
or to start another copy of the process.
.It Pa 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.
.It Pa cmdline
Process command line parameters, separated by NULs.
.It Pa note
Not implemented.
.It Pa notepg
Not implemented.
.It Pa regs
Allows read and write access to the process's register set.
This file contains a binary data structure
.Dv "struct regs"
defined in
.Aq Pa machine/reg.h .
.Pa regs
can only be written when the process is stopped.
.It Pa fpregs
The floating point registers as defined by
.Dv "struct fpregs"
in
.Aq Pa machine/reg.h .
.Pa fpregs
is only implemented on machines which have distinct general
purpose and floating point register sets.
.It Pa status
The process status.
This file is read-only and returns a single line containing
multiple space-separated fields as follows:
.Pp
.Bl -bullet -compact
.It
Command name.
.It
Process ID.
.It
Parent process ID.
.It
Process group ID.
.It
Session ID.
.It
.Ar major,minor
of the controlling terminal, or
.Dv -1,-1
if there is no controlling terminal.
.It
List of process flags:
.Dv ctty
if there is a controlling terminal,
.Dv sldr
if the process is a session leader, or
.Dv noflags
if neither of the other two flags are set.
.It
Process start time in seconds and microseconds,
comma separated.
.It
User time in seconds and microseconds,
comma separated.
.It
System time in seconds and microseconds,
comma separated.
.It
Wait channel message.
.It
Process credentials consisting of
the effective user ID
and the list of groups (whose first member
is the effective group ID),
all comma separated.
.El
.El
.Pp
In a normal debugging environment,
where the target is fork/exec'd by the debugger,
the debugger should fork and the child should stop
itself (with a self-inflicted
.Dv SIGSTOP
for example).
The parent should issue a
.Dv wait
and then an
.Dv attach
command via the appropriate
.Pa ctl
file.
The child process will receive a
.Dv SIGTRAP
immediately after the call to exec (see
.Xr execve 2 ) .
.Pp
Statistics reported by
.Xr df 1
on a procfs filesystem will indicate virtual memory used/available instead of
.Sq disk space ,
and the number of process slots used/allocated instead of
.Sq inodes .
The block size of the filesystem is the system page size.
.Sh FILES
.Bl -tag -width /proc/curproc -compact
.It Pa /proc/#
.It Pa /proc/curproc
.It Pa /proc/curproc/ctl
.It Pa /proc/curproc/file
.It Pa /proc/curproc/mem
.It Pa /proc/curproc/note
.It Pa /proc/curproc/notepg
.It Pa /proc/curproc/regs
.It Pa /proc/curproc/fpregs
.It Pa /proc/curproc/status
.El
.Sh SEE ALSO
.Xr mount 2 ,
.Xr sigaction 2 ,
.Xr fstab 5 ,
.Xr mount 8 ,
.Xr umount 8
.Sh HISTORY
The
.Nm
utility first appeared in
.Bx 4.4 .
.Sh CAVEATS
This filesystem may not be NFS-exported
since most of the functionality of
.Dv procfs
requires that state be maintained.