The lpc command is used to examine and control the print server operation. The lpc status command displays the administrative status of a print queue. The lpd program caches status and job information in order to improve performance. The lpc flush command will flush the cached information and cause the server to regenerate it. The lpc enable and lpc disable commands enable or disable spooling to the print queue, and the lpc stop and lpc start commands stop and start printing (or transfers) of jobs in the print queue.
Let's look at the status displayed when we use these commands:
h4: {120} % lpc status
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 enabled enabled 0 none none
h4: {121} % lpc status all
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 enabled enabled 0 none none
lp2@h4 enabled enabled 0 none none
h4: {122} % lpc
lpc>status
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 enabled enabled 0 none none
lpc>status all
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 enabled enabled 0 none none
lp2@h4 enabled enabled 0 none none
lpc>quit
The lpc command can be used in command line or interactive mode as shown above. When used with no parameters it will run in interactive mode, reading one or more commands from its standard input (STDIN). The lpc status command shows the administrative status of the select print queue. The all queue name selects all print queues for display. As shown in the above example, both print queues have printing and spooling enabled and there are no jobs in the print queue. The Server and Subserver information shows if there is a process which is printing jobs, and its helper process that does the actual communication with the printer.
It might be puzzling at first why LPRng uses two processes for this operation, but the reason is very simple. Many operating system implementations have memory leaks that cause the actual process size to grow as it runs. This is especially true if a large number of databases such as the password, Domain Name Server, or other system database is consulted frequently with different queries. Since this is usually done quite a lot by the process which deals with the actual printing, the printing process would soon grow very large and then die when it could no longer obtain more memory. The Server process will fork or create a child process Subserver process that is responsible for the printing of a single job. When the job printing has been completed, the Subserver process will exit and the Server process will then create another child until there are no more jobs to be printed. The Redirect and Debug fields will be discussed in later sections.
Now let's use the basic spool queue control commands:
h4: {123} % lpc disable
Printer: lp@h4
lp@h4.private: disabled
h4: {124} % lpq
Printer: lp@h4 (spooling disabled)
Queue: no printable jobs in queue
h4: {125} % lpc enable
Printer: lp@h4
lp@h4.private: enabled
h4: {126} % lpq
Printer: lp@h4
Queue: no printable jobs in queue
h4: {127} % lpc stop
Printer: lp@h4
lp@h4.private: stopped
h4: {128} % lpq
Printer: lp@h4 (printing disabled)
Queue: no printable jobs in queue
h4: {129} % lpc start
Printer: lp@h4
lp@h4.private: started
h4: {130} % lpq
Printer: lp@h4
Queue: no printable jobs in queue
As we can see, the lpc command also reports on the status of the print queue. Let's see what happens when we print to a stopped queue:
h4: {131} % lpc stop
Printer: lp@h4
lp@h4.private: stopped
h4: {132} % lpr /tmp/hi
h4: {133} % lpr /tmp/hi /tmp/there
h4: {134} % lpq
Printer: lp@h4 (printing disabled)
Queue: 2 printable jobs
Server: no server active
Rank Owner/ID Class Job Files Size Time
1 papowell@h4+17920 A 17920 /tmp/hi 3 18:14:22
2 papowell@h4+17922 A 17922 /tmp/hi,/tmp/there 9 18:14:30
h4: {135} % lpc status
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 disabled enabled 2 none none
The lpc status shows that we have two jobs spooled. The Rank field shows the order, the Owner/ID shows the unique job ID that is assigned to the job and the Class field is the job class (this may be changed with the lpr -C class option). The Job field shows the job number assigned to this job in this particular spool queue. While the ID value never changes as a job moves through the LPRng system, the job number is specific to a particular spool queue and may change if a job is forwarded to another spool queue that has a job with the same job number. The Size field is the total number of printable bytes in the job, and the Time field shows the timestamp associated with the job.
Now let's start the print queue and watch what happens.
h4: {136} % lpc start
Printer: lp@h4
lp@h4.private: started
h4: {137} % lpq
Printer: lp@h4
Queue: 2 printable jobs
Server: pid 17928 active
Unspooler: pid 17929 active
Status: opening device '/tmp/lp' at 18:14:43.921
Rank Owner/ID Class Job Files Size Time
active papowell@h4+17920 A 17920 /tmp/hi 3 18:14:22
2 papowell@h4+17922 A 17922 /tmp/hi,/tmp/there 9 18:14:30
h4: {138} % lpq -ll
Printer: lp@h4
Queue: 2 printable jobs
Server: pid 17928 active
Unspooler: pid 17929 active
Status: printing job 'papowell@h4+17920' at 18:14:43.921
Status: no banner at 18:14:43.921
Status: printing data file 'dfA017920h4.private', size 57 at 18:14:43.922
Rank Owner/ID Class Job Files Size Time
active papowell@h4+17920 A 17920 /tmp/hi 3 18:14:22
2 papowell@h4+17922 A 17922 /tmp/hi,/tmp/there 9 18:14:30
The Rank value of the first job has been changed to active and there is new Status information. If we use lpq -ll we can see the times that the various print operations are carried out, and details of their success or failure.
We can also use the lpc command to see the status of a particular job. We can select jobs by the user name, the ID, or the job number. For example:
h4: {139} % lpc stop
Printer: lp@h4
lp@h4.private: stopped
h4: {140} % echo hi |lpr
h4: {141} % echo there | lpr
h4: {142} % echo test |lpr
h4: {143} % lpq
Printer: lp@h4 (printing disabled)
Queue: 3 printable jobs
Server: no server active
Status: job 'papowell@h4+17922' removed at 18:15:13.981
Rank Owner/ID Class Job Files Size Time
1 papowell@h4+17959 A 17959 (stdin) 3 18:23:24
2 papowell@h4+17962 A 17962 (stdin) 6 18:23:30
3 papowell@h4+17970 A 17970 (stdin) 5 18:23:35
h4: {144} % lpq 17970
Printer: lp@h4 (printing disabled)
Queue: 3 printable jobs
Server: no server active
Status: job 'papowell@h4+17922' removed at 18:15:13.981
Rank Owner/ID Class Job Files Size Time
3 papowell@h4+17970 A 17970 (stdin) 5 18:23:35
h4: {145} % lpq papowell
Printer: lp@h4 (printing disabled)
Queue: 3 printable jobs
Server: no server active
Status: job 'papowell@h4+17922' removed at 18:15:13.981
Rank Owner/ID Class Job Files Size Time
1 papowell@h4+17959 A 17959 (stdin) 3 18:23:24
2 papowell@h4+17962 A 17962 (stdin) 6 18:23:30
3 papowell@h4+17970 A 17970 (stdin) 5 18:23:35
h4: {146} % lpq -s 17970
lp@h4 1 jobs
h4: {147} % lpq -s papowell
lp@h4 3 jobs
h4: {148} % lpq -s nobody
lp@h4 0 jobs
We use lpq -Pqueuename to select a specific print queue and lpq -a or lpq -Pall to select all queues:
h4: {149} % lpc -a stop
Printer: lp@h4
lp@h4.private: stopped
Printer: lp2@h4
lp2@h4.private: stopped
h4: {150} % lpc -Pall start
Printer: lp@h4
lp@h4.private: started
Printer: lp2@h4
lp2@h4.private: started
You can use the lpc command in interactive mode:
h4: {151} % lpc
lpc>status
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 enabled enabled 3 17990 17993
lpc>status all
Printer Printing Spooling Jobs Server Subserver Redirect Status/(Debug)
lp@h4 enabled enabled 3 17990 17993
lp2@h4 enabled enabled 3 none none
lpc>stop lp
Printer: lp@h4
lp@h4.private: stopped
lpc>start lp
Printer: lp@h4
lp@h4.private: started
lpc>quit
The lpc topq command can be used to put a job (or jobs) at the head of the spool queue. This command is very useful when some job requires priority service. You can select the job by using the job number or the job ID.
h4: {152} % lpc topq lp 17970
Printer: lp@h4
lp: selected 'papowell@h4+17970'
lp@h4.private: started
h4: {153} % lpq
Printer: lp@h4
Queue: 3 printable jobs
Server: pid 17999 active
Rank Owner/ID Class Job Files Size Time
active papowell@h4+17970 A 17970 (stdin) 5 18:23:35
1 papowell@h4+17959 A 17959 (stdin) 3 18:23:24
2 papowell@h4+17962 A 17962 (stdin) 6 18:23:30