locks - A directory that contains lock files for communication devices and remote systems that prevent multiple attempts to use the same device or contact a remote system
Lock files are created by the uucico daemon, the cu command, the tip command, and the uugetty command in the /var/spool/locks directory. The files are created when the utility opens the serial line for communication.
The lock file locks the device or remote system so that another process cannot access it while it is in use. The file name of the lock file uses one of the following forms: LCK..device_name LCK..system_name Where device_name is the name of the device (such as ttyd0) and system_name is the name of the system (such as hera).
Normally, the process that creates a lock file will remove it when the process has finished using the line. However, it is possible for lock files to be left behind (for example: system crash, phone line disconnects unexpectedly). This situation has been accounted for and the commands that use lock files can handle the situation and overwrite these files, if appropriate.
Lock files contains the process ID (PID) of the process that created the lock.
The lock file is a data file; to see its contents, use the following
od -d lockfile
Where lockfile is the name of the file. For example: % od -d /var/spool/locks/LCK..ttyd0 0000000 06854 00000 0000004
In this example, the lock file (LCK..ttyd0) was created by the process with PID 6854.
Contains the uucico daemon and uugetty program. Contains the uucp, cu, and tip programs.
Commands: cu(1), od(1), tip(1), uucp(1), uugetty(8)
Daemons: uucico(8), delim off