.\" $FreeBSD$
.\" Written by Garrett Wollman
.\" This file is in the public domain.
.\"
.Dd September 22, 2009
.Dt PROCFS 5
.Os
.Sh NAME
.Nm procfs
.Nd process file system
.Sh SYNOPSIS
.Bd -literal
proc		/proc	procfs	rw 0 0
.Ed
.Sh DESCRIPTION
The process file system, or
.Nm ,
implements a view of the system process table inside the file system.
It is normally mounted on
.Pa /proc ,
and is required for the complete operation of programs such as
.Xr ps 1
and
.Xr w 1 .
.Pp
The
.Nm
provides a two-level view of process space, unlike the previous
.Fx 1.1
.Nm
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
.Pa curproc
which always refers to the process making the lookup request.
.Pp
Each node is a directory which contains the following entries:
.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:
.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 (which
need not be the sending 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 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 ) .
.Pp
The
.Xr procctl 8
utility can be used to clear tracepoints in a stuck process.
.It Pa dbregs
The debug registers as defined by
.Dv "struct dbregs"
in
.In machine/reg.h .
.Pa dbregs
is currently only implemented on the i386 architecture.
.It Pa etype
The type of the executable referenced by the
.Pa file
entry.
.It Pa 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
.Ql unknown .
.It Pa fpregs
The floating point registers as defined by
.Dv "struct fpregs"
in
.In machine/reg.h .
.Pa fpregs
is only implemented on machines which have distinct general
purpose and floating point register sets.
.It Pa map
A map of the process' virtual memory.
.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 note
Used for sending signals to the process.
Not implemented.
.It Pa notepg
Used for sending signal to the process group.
Not implemented.
.It Pa 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.
.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
.In machine/reg.h .
.Pa regs
can only be written when the process is stopped.
.It Pa rlimit
This is a read-only file containing the process current and maximum
limits.
Each line is of the format
.Ar rlimit current max ,
with -1
indicating infinity.
.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 , Ns Ar 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.
.It
the hostname of the jail in which the process runs, or
.Ql -
to indicate that the process is not running within a jail.
.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
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 /proc/curproc/XXXXXXX -compact
.It Pa /proc
normal mount point for the
.Nm .
.It Pa /proc/pid
directory containing process information for process
.Pa pid .
.It Pa /proc/curproc
directory containing process information for the current process
.It Pa /proc/curproc/cmdline
the process executable name
.It Pa /proc/curproc/ctl
used to send control messages to the process
.It Pa /proc/curproc/etype
executable type
.It Pa /proc/curproc/file
executable image
.It Pa /proc/curproc/fpregs
the process floating point register set
.It Pa /proc/curproc/map
virtual memory map of the process
.It Pa /proc/curproc/mem
the complete virtual address space of the process
.It Pa /proc/curproc/note
used for signaling the process
.It Pa /proc/curproc/notepg
used for signaling the process group
.It Pa /proc/curproc/osrel
the process osrel value
.It Pa /proc/curproc/regs
the process register set
.It Pa /proc/curproc/rlimit
the process current and maximum rlimit
.It Pa /proc/curproc/status
the process' current status
.El
.Sh EXAMPLES
To mount a
.Nm
file system on
.Pa /proc :
.Pp
.Dl "mount -t procfs proc /proc"
.Sh SEE ALSO
.Xr procstat 1 ,
.Xr mount 2 ,
.Xr sigaction 2 ,
.Xr unmount 2 ,
.Xr procctl 8 ,
.Xr pseudofs 9
.Sh AUTHORS
.An -nosplit
This manual page written by
.An Garrett Wollman ,
based on the description
provided by
.An Jan-Simon Pendry ,
and revamped later by
.An Mike Pritchard .