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PROCFS(5)		    BSD	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 previ-
     ous 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 de-
		     livered, a	breakpoint is hit, or the target process ex-
	     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 with-
	     out 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 ad-
	     dress which exist in the process can be accessed.	Reads and
	     writes to this file modify	the process.  Writes to	the text seg-
	     ment 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 maxi-
	     mum 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 ter-
		 minal,	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 pri-
     mary 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.

BSD				April 22, 2013				   BSD


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