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PROCFS(5)                 FreeBSD File Formats Manual                PROCFS(5)

     procfs - process file system

     proc            /proc   procfs  rw 0 0

     The process file system, or procfs, implements a view of the system
     process table inside the file system.  It is normally mounted on /proc,
     and is required for the complete operation of programs such as ps(1) and

     The procfs provides a two-level view of process space, unlike the
     previous FreeBSD 1.1 procfs 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
     curproc which always refers to the process making the lookup request.

     Each node is a directory which contains the following entries:

     Each directory contains several files:

     ctl     a write-only 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
             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)).

             The procctl(8) utility can be used to clear tracepoints in a
             stuck process.

     dbregs  The debug registers as defined by struct dbregs in
             <machine/reg.h>.  dbregs is currently only implemented on the
             i386 architecture.

     etype   The type of the executable referenced by the file entry.

     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 `unknown'.

     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.

     map     A map of the process' virtual memory.

     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    Used for sending signals to the process.  Not implemented.

     notepg  Used for sending signal to the process group.  Not implemented.

     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.

     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

     rlimit  This is a read-only file containing the process current and
             maximum limits.  Each line is of the format rlimit current max,
             with -1 indicating infinity.

     status  The process status.  This file is read-only and returns a single
             line containing multiple space-separated fields as follows:

             +o   command name
             +o   process id
             +o   parent process id
             +o   process group id
             +o   session id
             +o   device name of the controlling terminal, or a minus sign
                 (``-'') if there is no controlling terminal.
             +o   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.
             +o   the process start time in seconds and microseconds, comma
             +o   the user time in seconds and microseconds, comma separated.
             +o   the system time in seconds and microseconds, comma separated.
             +o   the wait channel message
             +o   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.
             +o   the hostname of the jail in which the process runs, or `-' to
                 indicate that the process is not running within a jail.

     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

     Each node is owned by the process's user, and belongs to that user's
     primary group, except for the mem node, which belongs to the kmem group.

     /proc                  normal mount point for the procfs.
     /proc/pid              directory containing process information for
                            process pid.
     /proc/curproc          directory containing process information for the
                            current process
     /proc/curproc/cmdline  the process executable name
     /proc/curproc/ctl      used to send control messages to the process
     /proc/curproc/etype    executable type
     /proc/curproc/file     executable image
     /proc/curproc/fpregs   the process floating point register set
     /proc/curproc/map      virtual memory map of the process
     /proc/curproc/mem      the complete virtual address space of the process
     /proc/curproc/note     used for signaling the process
     /proc/curproc/notepg   used for signaling the process group
     /proc/curproc/osrel    the process osrel value
     /proc/curproc/regs     the process register set
     /proc/curproc/rlimit   the process current and maximum rlimit
     /proc/curproc/status   the process' current status

     To mount a procfs file system on /proc:

           mount -t procfs proc /proc

     procstat(1), mount(2), sigaction(2), unmount(2), procctl(8), pseudofs(9)

     This manual page written by Garrett Wollman, based on the description
     provided by Jan-Simon Pendry, and revamped later by Mike Pritchard.

FreeBSD 11.0-PRERELEASE         April 22, 2013         FreeBSD 11.0-PRERELEASE


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