PGRAB(3PROC) Process Control Library Functions PGRAB(3PROC)

NAME


Pgrab - grab and control a process

LIBRARY


Process Control Library (libproc, -lproc)

SYNOPSIS


#include <libproc.h>

struct ps_prochandle *
Pgrab(pid_t pid, int flags, int *perr);

DESCRIPTION


The Pgrab() function attempts to grab the process identified by pid and
returns a handle to it that allows the process to be controlled,
interrogated, and manipulated. This interface only works with processes
that already exist. Use Pgrab_core(3PROC) for core files and
Pcreate(3PROC) to create processes.

A grabbed process undergoes the following changes unless flags is set to
the contrary:

+o The process is stopped

+o All other tracing flags are cleared

+o The grab is exclusive. If any existing handles to this process
exist or anyone else is using the underlying facilities of the
/proc file system to control this process, it will fail.

+o Unless the process is already stopped, the PR_RLC flag is set
indicating the process should run-on-last-close. Allowing the
process to resume running if its controlling process dies.

Grabbing a process is a destructive action. Stopping a process stops
execution of all its threads. The impact of stopping a process depends on
the purpose of that process. For example, if one stops a process that's
primarily doing computation, then its computation is delayed the entire
time that it is stopped. However, if instead this is an active TCP server,
then the accept backlog may fill causing connection errors and potentially
connection time out errors.

Special care must be taken to ensure that a stopped process continues, even
if the controlling process terminates. If the controlling process disables
the PR_RLC flag or the process was already stopped, then the process
remains stopped after the controlling process terminates. Exercise caution
when changing this behavior.

Many of these default behaviors can be controlled by passing values to the
flags argument. Values for flags are constructed by a bitwise-inclusive-OR
of flags from the following list:

PGRAB_RETAIN Indicates that any existing tracing flags on pid should
be retained. If this flag is not specified, they will
be cleared as part of creating the libproc handle for
this process.

Normally extant tracing flags are cleared when a
process is grabbed.

PGRAB_FORCE Indicates that the process should not be grabbed
exclusively. Care should be taken with this option.
If other consumers are manipulating the process, then
this may result in surprising behavior as the process
is being manipulated from multiple points of control at
the same time.

Normally an attempt will be made to grab the process
exclusively and fail if it is already in use.

PGRAB_RDONLY Indicates that the process should be grabbed in a read-
only fashion. This implies that both the PGRAB_RETAIN
and PGRAB_NOSTOP flags should be set. If a process is
opened read-only, then a caller can only read
information about a process and cannot manipulate it,
change its current state, or inject systems calls into
it.

Normally when a process is grabbed, it does so for both
reading and writing.

PGRAB_NOSTOP Do not stop a process as it is grabbed. Note, any
extant tracing flags on the process will still be
cleared unless the PGRAB_RETAIN flag has been set.

Normally a process is stopped as a result of grabbing
the process.

The perr argument must be a non-NULL pointer which will store a more
detailed error in the event that the Pgrab() function fails. A human-
readable form of the error can be obtained with Pgrab_error(3PROC).

Once a caller is done with the library handle it should call
Prelease(3PROC) to release the grabbed process. Failure to properly
release the handle may leave a process stopped and interfere with the
ability of other software to obtain a handle.

Permissions


Unprivileged users may grab and control their own processes only if both
the user and group IDs of the target process match those of the calling
process. In addition, the caller must have a super set of the target's
privileges. Processes with the PRIV_PROC_OWNER privilege may manipulate
any process on the system, as long as it has an equal privilege set. For
more details on the security and programming considerations, please see the
section PROGRAMMING NOTES in proc(4).

RETURN VALUES


Upon successful completion, the Pgrab() function returns a control handle
to the process. Otherwise, NULL is returned with perr containing the error
code.

ERRORS


The Pgrab() function will fail if:

G_BUSY The process pid is already being traced and the
PGRAB_FORCE flag was not passed in flags.

G_LP64 The calling process is a 32-bit process and process pid
is 64-bit.

G_NOFD Too many files are open. This is logically equivalent
to receiving EMFILE.

G_NOPROC The process referred to by pid does not exist.

G_PERM The calling process has insufficient permissions or
privileges to open the specified process. See
Permissions for more information.

G_SYS The process referred to by pid is a system process and
cannot be grabbed.

G_SELF The process referred to by pid is the process ID of the
caller and the PGRAB_RDONLY was not passed. A process
may only grab itself if it's read-only.

G_STRANGE An unanticipated system error occurred while trying to
grab the process file and create the handle. The value
of errno indicates the system failure.

G_ZOMB The process referred to by pid is a zombie and cannot be
grabbed.

INTERFACE STABILITY


Uncommitted

MT-LEVEL
MT-Safe

SEE ALSO


errno(3C), libproc(3LIB), Pfree(3PROC), Pgrab_core(3PROC),
Pgrab_error(3PROC), Pgrab_file(3PROC), Prelease(3PROC)

illumos May 11, 2016 illumos