This output indicates that the printer connected to the print server box can be
addressed via TCP socket on port 9100. By default, nmap only checks a number of
commonly known ports listed in /usr/share/nmap/nmap-services. To check all
possible ports, use the command nmap -p
from_port
-
to_port IP-address
. This
may take some time. For further information, refer to the man page of nmap.
Enter a command like
echo -en "\rHello\r\f" | netcat -w 1 IP-address port
cat file | netcat -w 1 IP-address port
to send character strings or les directly to the respective port to test if the
printer can be addressed on this port.
14.8.4 Defective Printouts without Error Message
For the print system, the print job is completed when the CUPS back-end completes
the data transfer to the recipient (printer). If further processing on the recipient fails
(for example, if the printer is not able to print the printer-specic data) the print
system does not notice this. If the printer is not able to print the printer-specic data,
select a PPD le that is more suitable for the printer.
14.8.5 Disabled Queues
If the data transfer to the recipient fails entirely after several attempts, the CUPS
back-end, such as USB or socket, reports an error to the print system (to cupsd). The
back-end determines how many unsuccessful attempts are appropriate until the
data transfer is reported as impossible. As further attempts would be in vain, cupsd
disables printing for the respective queue. After eliminating the cause of the problem,
the system administrator must reenable printing with the command cupsenable.
14.8.6 CUPS Browsing: Deleting Print Jobs
If a CUPS network server broadcasts its queues to the client hosts via browsing and
a suitable local cupsd is active on the client hosts, the client cupsd accepts print jobs
from applications and forwards them to the cupsd on the server. When cupsd on the
server accepts a print job, it is assigned a new job number. Therefore, the job number
on the client host is dierent from the job number on the server. As a print job is
usually forwarded immediately, it cannot be deleted with the job number on the
client host This is because the client cupsd regards the print job as completed as
soon as it has been forwarded to the server cupsd.
When it becomes desirable to delete the print job on the server, use a command
such as lpstat -h cups.example.com -o to determine the job number on the server,
provided the server has not already completed the print job (that is, sent it completely
to the printer). Using this job number, the print job on the server can be deleted:
cancel -h cups.example.com
queue-jobnumber
Printer Operation 177
