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.\"     @(#)mount_procfs.8      8.3 (Berkeley) 6/1/94
.\"
.\"
.Dd February 24, 2009
.Dt MOUNT_PROCFS 8
.Os
.Sh NAME
.Nm mount_procfs
.Nd mount the process file system
.Sh SYNOPSIS
.Nm
.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 .
The directory specified by
.Ar mount_point
is converted to an absolute path before use.
This command is normally executed by
.Xr mount 8
at boot time.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl o Cm 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
.Sx FILES
for more information.
.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' pid.
In addition, the special entries
.Pa curproc
and
.Pa self
reference the current process.
The
.Pa self
symlink appears for compatibility with the Linux procfs implementation.
.Pp
Each directory contains several files.
.Bl -tag -width status
.It Pa 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.
.It Pa ctl
a writeonly file which supports a variety of control operations.
Control commands are written as strings to the
.Pa ctl
file.
The control commands are:
.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
continue execution of the target process and
remove it from control by the debug process.
.It run
continue running the target process until
a signal is delivered, a breakpoint is hit, or the
target process exits.
.It step
single step the target process, with no signal delivery.
.It wait
wait for the target process to stop.
The target process must be stopped before
any of the run, step, or signal 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 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
.Dq / .
.It Pa fd/#
File descriptors which can be accessed through the file system.
See
.Xr fd 4
for more information.
.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' symbol table,
or to start another copy of the process.
.It Pa map
A map of the process' virtual memory.
.It Pa maps
A map of the process' virtual memory in a form like the
proc filesystem as implemented in Linux.
Note that the paths corresponding to file backed mappings will
not be present unless the kernel was built with the
NAMECACHE_ENTER_REVERSE option.
.It Pa 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.
.It Pa note
Not implemented.
.It Pa notepg
Not implemented.
.It Pa regs
Allows read and write access to the process' register set.
This file contains a binary data structure
.Dv "struct regs"
defined in
.Pa \*[Lt]machine/reg.h\*[Gt] .
.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
.Pa \*[Lt]machine/reg.h\*[Gt] .
.Pa fpregs
is only implemented on machines which have distinct general
purpose and floating point register sets.
.It Pa 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
.Dq / .
.It Pa status
The process status.
This file is readonly 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
a list of process flags:
.Dv ctty
if there is a controlling terminal,
.Dv sldr
if the process is a session leader,
.Dv noflags
if neither of the other two flags are set.
.It
the process start time in seconds and microseconds,
comma separated.
.It
the user time in seconds and microseconds,
comma separated.
.It
the system time in seconds and microseconds,
comma separated.
.It
the wait channel message
.It
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.
.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 ) .
.Sh FILES
.Bl -tag -width /proc/curproc -compact
.It Pa /proc/#
.It Pa /proc/#/cmdline
.It Pa /proc/#/ctl
.It Pa /proc/#/cwd
.It Pa /proc/#/exe
.It Pa /proc/#/file
.It Pa /proc/#/fpregs
.It Pa /proc/#/map
.It Pa /proc/#/maps
.It Pa /proc/#/mem
.It Pa /proc/#/note
.It Pa /proc/#/notepg
.It Pa /proc/#/regs
.It Pa /proc/#/root
.It Pa /proc/#/status
.It Pa /proc/curproc
.It Pa /proc/self
.El
.Pp
If the
.Cm linux
mount option is used, the following files are also available:
.Pp
.Bl -tag -width /proc/meminfo -compact
.It Pa /proc/#/stat
.It Pa /proc/cpuinfo
.It Pa /proc/devices
.It Pa /proc/meminfo
.It Pa /proc/mounts
.It Pa /proc/uptime
.El
.Sh SEE ALSO
.Xr mount 2 ,
.Xr sigaction 2 ,
.Xr unmount 2
.Sh HISTORY
The
.Nm
utility first appeared in
.Bx 4.4 .
.Sh BUGS
This filesystem may not be NFS-exported
since most of the functionality of
.Dv procfs
requires that state be maintained.