07-17-2019
I don't know of any OS that randomly picks the next PID to use when creating a new process. But, it is theoretically possible to do it that way.
Most of the systems I have worked on have a maximum PID value that is a configuration parameter. They start out assigning PIDs from 1 and increment the PID they want to assign by one every time a new process is created (e.g., by fork()), but before assigning that value, they check to see if that PID is currently in use. If it is in use, the OS tries again with the next possible PID until it finds one that is not in use. Using this method, you won't run into problems with PID recycling unless there are so many processes running on your system that you don't have many possible PIDs available that aren't in use.
Furthermore, if you have a ps utility that conforms to POSIX requirements, you can ask ps to just print the fields you want to see and not have to worry about some unexpected value in a field you aren't interested in containing what looks like a PID. (Look at your man page for the ps -o format option.)
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LEARN ABOUT MOJAVE
rwsnoop
rwsnoop(1m) USER COMMANDS rwsnoop(1m)
NAME
rwsnoop - snoop read/write events. Uses DTrace.
SYNOPSIS
rwsnoop [-jPtvZ] [-n name] [-p PID]
DESCRIPTION
This is measuring reads and writes at the application level. This matches the syscalls read, write, pread and pwrite.
Since this uses DTrace, only users with root privileges can run this command.
OPTIONS
-j print project ID
-P print parent process ID
-t print timestamp, us
-v print time, string
-Z print zone ID
-n name
process name to track
-p PID PID to track
EXAMPLES
Default output,
# rwsnoop
Print zone ID,
# rwsnoop -.Monitor processes named "bash", # rwsnoop -n bash
FIELDS
TIME timestamp, us
TIMESTR
time, string
ZONE zone ID
PROJ project ID
UID user ID
PID process ID
PPID parent process ID
CMD command name for the process
D direction, Read or Write
BYTES total bytes during sample
FILE filename, if file based. Reads and writes that are not file based, for example with sockets, will print "<unknown>" as the file-
name.
DOCUMENTATION
See the DTraceToolkit for further documentation under the Docs directory. The DTraceToolkit docs may include full worked examples with ver-
bose descriptions explaining the output.
EXIT
rwsnoop will run forever until Ctrl-C is hit.
AUTHOR
Brendan Gregg [Sydney, Australia]
SEE ALSO
rwtop(1M), dtrace(1M)
version 0.70 Jul 24, 2005 rwsnoop(1m)