There is no perfect solution to this problem. Someone else on the system might be running an identically named script. And pids do recycle.
Here is a quick script that illustrates my solution:
Is the script is functioning properly, it will create and delete the lockout.pid file correctly. If the lockout.pid file exists, then the process should also exist.
If the script is abruptly killed and cannot remove the lockout.pid file then the next instance of the script will detect it. The new instance will try to send signal zero to the old pid. If the script is not running as root, it will not be able to signal another user's process.
If the previous instance of the script finished normally, the new instance of the script cannot be fooled. If the previous instance of the script is still running, the new instance of the script cannot be fooled. These are the normal conditions we expect to find.
So to fool the script, first it must abort, second the pid must have recycled and the pid must now be in use by a new, unrelated process, and third, the new process be belong to the same user that is running the script. The third condition is lifted if root runs the script.
Problem
I have an application which basically runs lots of UNIX programs remotely, using the Telnet protocol. For each program it remotely executes, it stores the process ID (PID) for that process.
At regular intervals, I would like my application to take the PID for every process still... (5 Replies)
In my last job someone gave me the command to put in my .profile that let me know when a job I had running in the background finished. It was a word about 5 char long. I can't remember it! (4 Replies)
So, the script I've been working on, since I was starting to learn Shell scripting is now complete.
This was coded in ksh, and I am very proud of it.
What this script does, is syncs up uid's across the network. So if you have 10 servers, with 10 usernames with different UID's - this will... (1 Reply)
Hi frnds,
I want to know is there a way by which we can know that a C++ executable has finished its job in shell script.
My task is as follows:
1.Shell script calls a executable
2.Executable executes and performs its job of generating some reports.
Now i want my shell script to... (4 Replies)
Hi all,
I am writing a C shell script that starts a program. The program forks of several child processes. Only when all child processes are done, I want to archive my log files. Below is what I have so far, but unfortunately it doesn't work.
MyProgram
if (-e processes.txt) then
rm... (2 Replies)
Hi all,
I have a script that is monitoring a hot folder. This script works fine with one exception when the script is executed while a file is being copied to the hot folder.
What is the easiest method to check if the copy file is completed? I'd like to get the solution in bash :) (8 Replies)
I have a script which uses cli curl to download the source code of a webpage and then tests if a specific string exists in the source.
The problem is that the website has a slow response, so the eval expression hasn't completed when the test starts.
The test returns a negative, and the curl... (8 Replies)
I am running a macro script from the command line. But the script doesn't wait until the task has finished.
firefox imacros://run/?m=macro_script.iim
firefox imacros://run/?m=macro_script2.iim
How do I get it to wait until the macro has been completed?
I am using imacros, a firefox... (1 Reply)
Hello,
I have a script that is running multiple instances of an application in parallel.
# learn on f0
emergent -nogui -p $ScriptLoc/$PROJ fold_tag=f0 &
sleep 5
# learn on f1
emergent -nogui -p $ScriptLoc/$PROJ fold_tag=f1 &
sleep 5
# learn on f2
emergent -nogui -p... (4 Replies)
Heyas,
Since this question (similar) occur every now and then, and given the fact i was thinking about it just recently (1-2 weeks) anyway, i started to write something :p
The last point for motivation was... (17 Replies)
Discussion started by: sea
17 Replies
LEARN ABOUT X11R4
wait
wait(1) User Commands wait(1)NAME
wait - await process completion
SYNOPSIS
/bin/sh
wait [pid...]
/bin/jsh /bin/ksh /usr/xpg4/bin/sh
wait [pid...]
wait [ % jobid...]
/bin/csh
wait
DESCRIPTION
The shell itself executes wait, without creating a new process. If you get the error message cannot fork,too many processes, try using the
wait command to clean up your background processes. If this doesn't help, the system process table is probably full or you have too many
active foreground processes. There is a limit to the number of process IDs associated with your login, and to the number the system can
keep track of.
Not all the processes of a pipeline with three or more stages are children of the shell, and thus cannot be waited for.
/bin/sh, /bin/jsh
Wait for your background process whose process ID is pid and report its termination status. If pid is omitted, all your shell's currently
active background processes are waited for and the return code will be 0. The wait utility accepts a job identifier, when Job Control is
enabled (jsh), and the argument, jobid, is preceded by a percent sign (%).
If pid is not an active process ID, the wait utility will return immediately and the return code will be 0.
csh
Wait for your background processes.
ksh
When an asynchronous list is started by the shell, the process ID of the last command in each element of the asynchronous list becomes
known in the current shell execution environment.
If the wait utility is invoked with no operands, it will wait until all process IDs known to the invoking shell have terminated and exit
with an exit status of 0.
If one or more pid or jobid operands are specified that represent known process IDs (or jobids), the wait utility will wait until all of
them have terminated. If one or more pid or jobid operands are specified that represent unknown process IDs (or jobids), wait will treat
them as if they were known process IDs (or jobids) that exited with exit status 127. The exit status returned by the wait utility will be
the exit status of the process requested by the last pid or jobid operand.
The known process IDs are applicable only for invocations of wait in the current shell execution environment.
OPERANDS
The following operands are supported:
One of the following:
pid The unsigned decimal integer process ID of a command, for which the utility is to wait for the termination.
jobid A job control job ID that identifies a background process group to be waited for. The job control job ID notation is applicable
only for invocations of wait in the current shell execution environment, and only on systems supporting the job control option.
USAGE
On most implementations, wait is a shell built-in. If it is called in a subshell or separate utility execution environment, such as one of
the following,
(wait)
nohup wait ...
find . -exec wait ... ;
it will return immediately because there will be no known process IDs to wait for in those environments.
EXAMPLES
Example 1: Using A Script To Identify The Termination Signal
Although the exact value used when a process is terminated by a signal is unspecified, if it is known that a signal terminated a process, a
script can still reliably figure out which signal is using kill, as shown by the following (/bin/ksh and /usr/xpg4/bin/sh):
sleep 1000&
pid=$!
kill -kill $pid
wait $pid
echo $pid was terminated by a SIG$(kill -l $(($?-128))) signal.
Example 2: Returning The Exit Status Of A Process
If the following sequence of commands is run in less than 31 seconds (/bin/ksh and /usr/xpg4/bin/sh):
sleep 257 | sleep 31 &
jobs -l %%
then either of the following commands will return the exit status of the second sleep in the pipeline:
wait <pid of sleep 31>
wait %%
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of wait: LANG, LC_ALL, LC_CTYPE, LC_MES-
SAGES, and NLSPATH.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), jobs(1), ksh(1), sh(1), attributes(5), environ(5), standards(5)SunOS 5.10 12 Dec 1997 wait(1)