This documentation is intended for internal Performance Co-Pilot
(PCP) developer use.
These interfaces are not part of the PCP APIs that are guaranteed to
remain fixed across releases, and they may not work, or may provide
different semantics at some point in the future.
Within the libraries and applications of the Performance Co-Pilot
(PCP) these routines are provide a convenient and safe alternative to
system(3) for executing commands in a separate process.
Use __pmProcessAddArg to register the executable and command
arguments in order. handle should be set to NULL before the first
call to __pmProcessAddArg for a particular command execution and it
will be set to an opaque pointer to data structures that are
manipulated in __pmProcessAddArg, __pmProcessExec and the related
When called with handle set to NULL arg is treated as the name of the
command to be executed and subsequent calls (if any) are for the
arguments to that command. The name of the command can be a full
pathname, or the name of an executable that can be found on the
current $PATH as per the rules of execvp(2) that is used by
__pmProcessUnpickArgs is a convenience wrapper to assist conversion
of code that assumes the command is a shell command that has been
prepared for use with system(3) or popen(3) in existing code. The
arguments in command are picked off one-by-one and used to call
__pmProcessAddArgs. The parser is simple, as the routine is designed
for simple shell command syntax, where arguments are separated by one
or more spaces but embedded spaces within an argument are allowed if
the arguement is enclosed in single or double quotes. More advanced
shell syntax like escape characters and input-output redirection are
Once all the command name and arguments have been registered calling
__pmProcessExec uses a fork(2) and execvp(2) sequence to execute the
The argument toss may be used to assign some or all of the standard
I/O streams for the command to /dev/null - specifically toss is
either PM_EXEC_TOSS_NONE to keep all I/O streams the same as the
parent process, else the bit-wise or of PM_EXEC_TOSS_STDIN and/or
PM_EXEC_TOSS_STDOUT and/or PM_EXEC_TOSS_STDERR to reassign stdin,
stdout and stderr respectively. PM_EXEC_TOSS_ALL is a convenience
macro equivalent to PM_EXEC_TOSS_STDIN | PM_EXEC_TOSS_STDOUT |PM_EXEC_TOSS_STDERR.
The wait argument should be PM_EXEC_WAIT if __pmProcessExec should
wait for completion of the command and harvest the exit status, else
PM_EXEC_NOWAIT in which case __pmProcessExec returns immediately
(effectively running the command in the background).
Nested calling of __pmProcessExec and/or __pmProcessPipe(3) is not
allowed. Once __pmProcessAddArg is called with handle set to NULL to
start the registration and execution sequence any attempt to start a
second registration sequence will be blocked until the first one is
completed by calling __pmProcessExec or __pmProcessPipe(3).
If successful __pmProcessAddArg returns 0. Other conditions are rare
(e.g. alloc failure) and are indicated by a return value that can be
decoded using pmErrStr(3).
__pmProcessUnpickArgs returns 0 on success. In the case of an
unterminated string, a message is generated and PM_ERR_GENERIC is
returned. Other return values less than 0 indicate a more serious
error and the value can be decoded using pmErrStr(3).
The return status from __pmProcessExec is more complicated. If
either PM_EXEC_NOWAIT is specified, or the command completes with an
exit status of 0, the return value is 0. Return values less than 0
indicate a more serious error and the value can be decoded using
pmErrStr(3). If the command was executed, but did not exit with
status of 0 then the return value is an encoding of the waitpid(2)
status as follows: 2000 if something unknown went wrong, else if 1000
+ signal number of the command was killed or stopped by a signal,
else the exit status of the command.
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
email@example.com. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2020-07-14. (At that time, the date of the most recent commit that
was found in the repository was 2020-07-14.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
Performance Co-Pilot PCP PMPROCESSEXEC(3)