freebsd-src/sbin/mount_procfs/mount_procfs.8

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.\"	@(#)mount_procfs.8	8.2 (Berkeley) 3/27/94
.\"
.\"
.Dd March 27, 1994
.Dt MOUNT_PROCFS 8
.Os BSD 4.4
.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 mount_procfs
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 indent
.It Fl o
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.
.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 entry
.Pa curproc
references the current process.
.Pp
Each directory contains several files.
.Bl -tag -width status
.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 (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 ).
.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 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
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 <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
.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 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/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 sigaction 2 ,
.Xr mount 2 ,
.Xr unmount 2 ,
.Sh CAVEATS
No
.Pa .
and
.Pa ..
entries appear when listing the contents of the
.Pa /proc
directory.
This makes sense in the context of this filesystem, but is inconsistent
with usual filesystem conventions.
However, it is still possible to refer to both
.Pa .
and 
.Pa ..
in a pathname.
.Pp
This filesystem may not be NFS-exported
since most of the functionality of
.Dv procfs
requires that state be maintained.
.Sh HISTORY
The
.Nm mount_procfs
utility first appeared in 4.4BSD.