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. This command is normally executed by mount(8) at boot time.

The options are as follows:

-o  Options are specified with a -o flag followed by a comma separated string of options. See the mount(8) man page for possible options and their meanings.

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 curproc references the current process.

Each directory contains several files.

ctl a writeonly file which supports a variety of control operations. Control commands are written as strings to the ctl file. The control commands are:
    attach
        stops the target process and arranges for the sending process to become the debug control process.
    detach
        continue execution of the target process and remove it from control by the debug process (which need not be the sending process).
    run continue running the target process until a signal is delivered, a breakpoint is hit, or the target process exits.
    step
        single step the target process, with no signal delivery.
    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.

    The string can also be the name of a signal, lower case and without the SIG prefix, in which case that signal is delivered to the process (see sigaction(2) ).

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.

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.

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.

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.

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 SIGSTOP for example). The parent should issue a wait and then an attach command via the appropriate ctl file. The child process will receive a SIGTRAP immediately after the call to exec (see execve(2) ).

FILES
/proc/#
/proc/curproc
/proc/curproc/ctl
/proc/curproc/file
/proc/curproc/mem
/proc/curproc/note
/proc/curproc/notepg
/proc/curproc/regs
/proc/curproc/fpregs
/proc/curproc/status

SEE ALSO
sigaction(2), mount(2), unmount(2),

CAVEATS
No ~. and.. entries appear when listing the contents of the /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 ~. and.. in a pathname.

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

HISTORY
The mount_procfs utility first appeared in 4.4BSD.