16 lines
774 B
Text
16 lines
774 B
Text
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The shlock command can create or verify a lock file on behalf of a
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shell or other script program. When it attempts to create a lock
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file, if one already exists, shlock verifies that it is or is not
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valid. If valid, shlock will exit with a non-zero exit code. If
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invalid, shlock will re- move the lock file, and create a new one.
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shlock uses the rename(2) system call to make the final target lock
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file, which is an atomic operation (i.e. "dot locking", so named for
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this mech- anism's original use for locking system mailboxes). It
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puts the process ID ("PID") from the command line into the requested
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lock file.
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shlock verifies that an extant lock file is still valid by using
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kill(2) with a zero signal to check for the existence of the process
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that holds the lock.
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