V10/man/man4/proc.4

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.TH PROC 4
.CT 2 proc_man
.SH NAME
proc \- process file system
.SH SYNOPSIS
.B #include <sys/types.h>
.B #include <sys/proc.h>
.br
.B #include <sys/pioctl.h>
.SH DESCRIPTION
.I Proc
is a file system that contains memory images of each
running process in the system.
The name of each entry in the
.F /proc
directory is the process
id of the subject process, expressed in decimal with
optional leading zeros.
Each process file is owned by the userid of the subject process.
The file mode includes read and write permission for
the owner if that userid has read
access to the associated text file; all other permission bits
are zero.
The file size is
the sum of the sizes of virtual memory segments
in the subject process.
.PP
The subject process is unaffected, except that setuid bits
will be ignored if it does an
.IR exec (2).
(Setuid bits are also ignored if the
.IR exec "ing"
process has traced signals, or stops on
.IR exec ;
see the description of
.B PIOCSMASK
and
.B PIOCSEXEC
below.)
.PP
Data may be transferred
from or to any locations in the subject's address space through
.IR lseek (2),
.IR read (2),
and
.IR write .
The
.I text segment
begins at address 0; the
.I data segment
starts above the text.
The
.I user area
extends downward below address 0x80000000, and is
.B UPAGES*NBPG
bytes long (see the header files listed below);
the
.I stack segment
grows downward below the user area.
The text, data, and stack sizes
may be determined from the process's
.L proc
structure (see
.B PIOCGETPR
below).
It is an error to access addresses between data and stack.
No read or write may span a segment boundary;
in the user area only the locations of saved user registers
are writable.
.PP
.IR Ioctl (2)
calls control the subject process.
The third argument usually points to an integer.
The 
.I ioctl
codes are:
.TF PIOCSMASK
.TP
.B PIOCSTOP
Send signal
.B SIGSTOP
to the process, and wait for it to
enter the stopped state.
.TP
.B PIOCWSTOP
Wait for the process to stop.
.TP
.B PIOCRUN
Make the process runnable again after a stop.
.TP
.B PIOCSMASK
Define
a set of signals to be traced.
The process will stop when it receives any signal whose number,
as given in
.IR signal (2),
corresponds to a 1-bit in the given integer,
with the least significant bit counted as 1.
The traced state and mask bits are inherited by the child of a
.IR fork (2).
When the process file is closed, the mask becomes zero, but
the traced state persists.
.TP
.B PIOCSEXEC
Cause the process to stop after
.IR exec (2).
This condition is inherited across
.IR fork (2)
and persists when the process file is closed.
.TP
.B PIOCREXEC
Reverse the effect of
.BR PIOCSEXEC .
.TP
.B PIOCCSIG
Clear the subject's currently pending signal (if any).
.TP
.B PIOCKILL
Set the subject's currently pending signal to a given number.
.TP
.B PIOCOPENT
Return a read-only file descriptor
for the subject process's text file.
(Thus a debugger can find the
symbol table without knowing the name of the text file.)
.TP
.B PIOCNICE
Increment the
priority of the subject process by a given amount
as if by
.IR nice (2).
.TP
.B PIOCGETPR
Copy the subject's
.B proc
structure (see
.BR <sys/proc.h> )
from the kernel process table into an area pointed to
the third argument.
(This information, which resides in system space, is not accessible
via a normal read.)
.PD
.PP
Any system call is guaranteed to be atomic with respect to the 
subject process,
but nothing prevents more than one
process from opening and controlling the same subject.
.PP
The following header files are useful in analyzing
.I proc
files:
.PP
.TF <sys/param.h>
.TP
.B <signal.h>
list of signal numbers
.TP
.B <sys/param.h>
size parameters
.TP
.B <sys/types.h>
special system types
.TP
.B <sys/user.h>
user structure
.TP
.B <sys/proc.h>
proc structure
.TP
.B <sys/reg.h>
locations of saved user registers
.TP
.B <sys/pioctl.h>
ioctl codes for
.I proc
files
.PD
.SH FILES
.F /proc/*
.SH SEE ALSO
.IR adb (1),
.IR ps (1), 
.IR hang (1),
.IR fmount (2),
.IR signal (2),
.IR mount (8),
.IR pi (9.1)
.SH DIAGNOSTICS
These errors can occur in addition to the
errors normally associated with the file system; see
.IR intro (2):
.TF ENOENT
.TP
.B ENOENT
The subject process has exited.
.TP
.B EIO
The subject process has attempted I/O at an illegal address.
.TP
.B EBUSY
The subject is in the midst of changing virtual memory
attributes, or has pages locked for physical I/O.
.TP
.B ENOSPC
A write has been attempted on a shared text segment and there
is no room on the swap space to make a copy.
.TP
.B EPERM
A non-super-user has attempted to better
the subject's priority with
.BR PIOCNICE .
.SH BUGS
A process must be swapped in for reading and writing (but not
.IR ioctl );
this may cause
a noticeable delay.
.br
The spectrum of states which result in 
.B EBUSY
is too conservative.
.br
A process loaded from a text file with magic number 0407 does not have as
a read-only text segment; in this (presumably rare) case
.B PIOCOPENT
does not work, and the process is accessible even if the
text file is read-only.
.br
The interface involves too many VAX-specific magic numbers.