System Administration Guide
Chapter 7, Connecting to other computers with UUCP

The UUCP spool directory contents

The UUCP spool directory contents

The following describes all files and subdirectories of the UUCP spool directory. These files are created in spool directories to lock devices, hold temporary data, or keep information about remote transfers or executions.

TM. (temporary data file)

These data files are created by UUCP processes under the spool directory (that is, /usr/spool/uucp/system) when a file is received from another computer. The system directory has the same name as the remote computer that is sending the file. The names of the temporary data files have the format: 

TM.pid.ddd

where pid is a process-ID and ddd is a sequential three-digit number starting at 0.

When the entire file is received, the TM.pid.ddd file is moved to the pathname specified in the C.sysnxxxx file (discussed below) that caused the transmission. If processing is abnormally terminated, the TM.pid.ddd file may remain in the system directory. These files should be automatically removed by uuclean.

LCK. (lock file)

Lock files are created in the /usr/spool/uucp directory for each device in use. Lock files prevent duplicate conversations and multiple attempts to use the same calling device. The names of lock files have the format:

LCK..str

where str is either a device or computer name. These files may remain in the spool directory if the communications link is unexpectedly dropped (usually on computer crashes). The lock files are ignored (removed) after the parent process is no longer active. The lock file contains the process ID of the process that created the lock. The lock file is always named by converting the last letter to lowercase (meaning non-modem control) to avoid possible conflicts if the same line is specified both as modem-control and non-modem-control. For example, the lock on /dev/tty1A is named LCK..tty1a. 

C. (work file)

Work files are created in a spool directory on the local computer when work (file transfer or remote command execution) is queued for a remote computer. The names of work files have the format:

C.sysnxxxx

where sys is the name of the remote computer, n is the ASCII character representing the grade (priority) of the work, and xxxx is the four-digit job sequence number assigned by UUCP. Work files contain the following information:

D.(data file) 

Data files are created in the spool directory on both the local and remote computers when it is specified in the command line to copy the source file to the spool directory. The names of data files have the following format:

D.systmxxxxyyy

where systm is the first five characters in the name of the remote computer, xxxx is a four-digit job sequence number assigned by uucp. The four-digit job sequence number may be followed by a subsequence number yyy which is used when there are several D. files created for a work (C.) file.

X. (execute file)

Execute files are created in the spool directory on the remote computer prior to remote command executions. The names of execute files have the following format:

X.sysnxxxx

where sys is the name of the remote computer, n is the character representing the grade (priority) of the work, and xxxx is a four-digit sequence number assigned by UUCP. Execute files contain the following information: