15 What are locks?

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Locks are simply a file saying that a particular device is in use. They are kept in /usr/spool/uucp. Locks are named LCK..<name>, where <name> is either a device name, or a UUCP site name. Certain processes create these locks so that they can have exclusive access to devices, for instance if you dial out on your modem, a lock will appear telling other processes that someone is using the modem already. Locks mainly contain the PID of the process that has locked the device. Most programs look at the lock, and try to determine if that lock is still valid by checking the process table for the process that has locked the device. If the lock is found to be valid, the program should exit. If not, some programs remove the stale lock, and use the device, creating their own lock in the process.

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