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