How to debug printing problems

Foreword

If you are experiencing a problem with printing, please take a look at the common bugs page before filing a bug. If the problem you are seeing is not listed there or none of the workarounds seem to help, please consider filing a bug report to help us make Fedora run better on your hardware.

Identifying your problem area

Printing issues can be fairly complex and active cooperation or lots of data can be requested from reporter by maintainer to helping maintainer to at least understand and (if it is not hardware specific issue) reproduce the issue, so please have a patience and try to narrow the problem as much you are able to for maintainers.

There can be:

• issues with seeing or connecting to the printer (it can be cups backend issues, avahi issues, libusb issues, cups-browsed issues),
• accessibility issues (correct/wrong setup in cupsd.conf or its bad interpretation by cupsd daemon, bad cooperation with NIS, SSSD...),
• printing with help of samba (issues with smb backend, which is part of samba) or with samba authenticated through Kerberos (samba_krb5_printing),
• issues with filters used during filtering the document into document format supported by printer, which influence how or if the document will be printed (issue with filters - pdftops, pdftopdf, pstops, bannertopdf etc. - or issues with binaries or libraries which filters uses - libgs, qpdf, poppler...),
• issues with Postscript Printer Description files, which are old way of defining printers capabilities like supported page sizes, borders etc...

Not mentioning possible limitations or issues in firmware or hardware of printer itself, so any kind of data or narrowing the issue is welcomed.

The best start is to attach files with logs described further down.

CUPS logging

All CUPS logging is redirected to journal by default since Fedora 28 (there was a redirecting of error_log to journal by default before Fedora 28, since Fedora 20). Printing troubleshooter doesn't have a feature to get logs from systemd journal yet, so CUPS logs need to be acquired by following steps.

We need to define two different ways of capturing incident-bound CUPS whole logs - the one if the broken print queue isn't provided by HPLIP and the other if it is. They differs in the filter option of journald - if you use non-HPLIP queue for debugging, it is okay to gather the logs from cups systemd unit (by '-u cups'), because all error messages are correctly redirected to cups systemd unit logging and they are accessible in the output after unit filtering. HPLIP libraries are not implemented to do the same (upstream is unresponsive to accept a potencial fix into the project and the issue is not critical enough to drag a downstream patch forever), so their messages aren't marked for cups systemd unit and they're filtered out after calling journald with '-u cups'. For such queues journald log without filtering is required.

Note:

Incident-bound journald log without filtering is required only for HPLIP print queues (their device uri starts with hp://) and it is unwanted for other queues, because it can be hard to read in larger cases. Please attach incident-bound journald log only when it is necessary.

Location of CUPS logging

CUPS logging is located in the system journal by default, but the logging into a file can be set in /etc/cups/cups-files.conf with directive 'ErrorLog'. If you want to change the default settings, then the name of the logging file is irrelevant, but it is recommended to put the file into path '/var/log/cups', otherwise SELinux will block cupsd from accessing it.

Setting the logging to a file has following cons (without further operations):

• unable to get only logs connected to a job without chaining more commands
• unable to get logs for specified time frame without chaining more commands

For capturing a incident-bound logs 'tail -f' can be used e.g.:

tail -f /var/log/cups/error_log

Enable CUPS debug logging

Enable full debugging information with:

sudo sed -i 's,LogLevel warn,LogLevel debug2,' /etc/cups/cupsd.conf

CUPS job log

IMPORTANT If the problem appears when you sent document to print or if you are trying to, capture logs for this job. If the job log is available, its attaching is REQUIRED.

Prepare CUPS for job logging

For being able to see specific job log, please turn on:

PreserveJobFiles Yes

in your /etc/cups/cupsd.conf file and restart cup service. Do not forget to remove the line after you are done with debugging. 'lpstat -W all' seems to be empty after printing if you do not enable the directive.

Get a job log for a specific Job ID

To capture job log you need to know Job ID (JID) of the job - it is a number which together with print queue name specifies the job as request ID - for getting logs specific for the job.

Job ID can be seen in terminal if you send a document to print by lp command:

$ lp -d <print_queue_name> <file1> ... <fileN>
request id is <print_queue_name>-<JID> (N file(s))

Or when you list jobs (see man lpstat) - the latest job is at the end:

$ lpstat -W all
...
<print_queue_name>-<JID>           <user>           1024   Wed 11 Jan 2017 05:52:19 PM CET

You can get the latest job logs automatically (if you have awk installed and lpstat -W all returns jobs) by:

$ journalctl -u cups JID=`lpstat -W all | awk '{print $1}' | awk -F '-' '{print $NF}' | tail -n 1` > cups_job_log

Or manually, if you found JID by yourself:

journalctl -u cups JID=<JID> > cups_job_log

Incident-bound cupsd log (broken print queue isn't HPLIP supported)

Sometimes we cannot bind the error with a specific print job, so the job log is uneffective. Incident-bound cupsd log is needed.

How to start to capture incident-bound cupsd logging

In new terminal/terminal tab, please issue:

journalctl -f -u cups > cups_whole_log

How to get incident-bound cupsd logging

After you trigger the error condition you are trying to diagnose e.g. printing something, try to find a printer via lpinfo etc., you terminate capturing incident-bound cupsd log from step above by ctrl+c.

Incident-bound cupsd log (broken print queue is HPLIP supported)

Unfortunately, HPLIP libraries don't log into CUPS unit in journal, so if your print queue is installed with HPLIP driver (its device uri starts with hp://), we need incident-bound journal log.

How to start to capture incident-bound journal logging

In new terminal/terminal tab, please issue:

journalctl -f > journal_whole_log

How to get incident-bound journal logging

After you trigger the error condition you are trying to diagnose e.g. printing something, running HP script etc., you terminate capturing incident-bound journal log from step above by ctrl+c.

Turning off debug logging

Please attach cups_job_log for the problematic job, cups_whole_log or journal_log if you caught whole cupsd log during the problematic event to bug report as an attachment.

Then to turn off debugging information, do this:

sudo sed -i 's,LogLevel debug2,LogLevel warn,' /etc/cups/cupsd.conf

More commands for working with systemd-journald

View the log messages with:

journalctl -u cups -e

or:

journalctl -u cups --since=...

To filter out messages relating to a specific job ID, use:

journalctl -u cups JID=...

(tab completion will show you which job IDs have log messages)

cups-browsed logging

cups-browsed daemon was introduced in Fedora around cups-1.5 version. It can browse Bonjour broadcasts, CUPS broadcasts (deprecated) and LDAP servers for printers and create or remove local queues pointing to those printers. It can creates broadcasts of local CUPS queues, but it is marked as deprecated.

For setting debug logging on you need to add:

DebugLogging stderr

to /etc/cups/cups-browsed.conf.

The logs will be available in system journal after cups-browsed restart.

HPLIP scripts debug logging

Python scripts from HPLIP (e.g. hp-setup, hp-clean, hp-scan) have debug logging redirected to the standard error file descriptor, so they are not logged in journal. For getting their debug logging, run the script with -ldebug parameter e.g.:

$ hp-setup -ldebug -i

and reproduce the issue. Then copy the messages from terminal into hp_script_log. Please attach the file to the bugzilla ticket too.

What make and model is my printer?

Each different printer has a model-specific Device ID. You can find out with the lpinfo command:

lpinfo -l -v

This command runs each of the backends in discovery mode, to get them to report devices they can automatically detect. This will output a series of blocks of lines, each one like this:

Device: uri = usb://HP/DESKJET%20990C?serial=U123456789AB
        class = direct
        info = HP DESKJET 990C
        make-and-model = HP DESKJET 990C
        device-id = MFG:HEWLETT-PACKARD;MDL:DESKJET 990C;CMD:MLC,PCL,PML;CLS:PRI
NTER;DES:Hewlett-Packard DeskJet 990C;SN:U123456789AB;S:00808880800010032C100000
0C2000000;P:0800,FL,B0;J:                    ;
        location = 

The line which identifies this particular model type is the long one that starts "device-id =" (shown here wrapping over three lines).

Note that if your printer cannot be automatically detected, you may still be able to find out the Device ID by running the appropriate backend with the printer hostname as the argument. The usb, parallel, snmp, and dnssd backends all try to report the actual Device ID given by the printer.

$ /usr/lib/cups/backend/snmp 10.34.18.3

network socket://10.34.18.3 "HP Color LaserJet CP2025dn" "HP Color LaserJet CP2025dn"
"MFG:Hewlett-Packard;CMD:PJL,PML,PCLXL,POSTSCRIPT,PCL;MDL:HP Color LaserJet CP2025dn;
CLS:PRINTER;DES:Hewlett-Packard Color LaserJet CP2025dn;MEM:MEM=55MB;COMMENT:RES=600x8;" "HP Color LaserJet CP2025dn" 

Device ID is in this case (see backend(7)) the last but one field.

Which print queues are available for me?

The queues on your machine can be permanent ones or temporary. CUPS is capable to list all available print queues on the local network (permanent and temporary queues) by:

$ lpstat -e

For permanent queues you are able to get more info with:

$ lpstat -t

Which driver am I using?

The PPD file for the printer queue can tell you which driver is in use. You can use this command to find out which driver is being used:

grep -H '^*NickName:' /etc/cups/ppd/*.ppd

You can also find this out using the system-config-printer application. Double-click on the icon for the queue and look at the Make and Model field.

To see the available drivers, click on the Change... button next to that field. You might find it useful to try another driver to see if that shows the same problem.

Driverless models

Most printers released since 2010 are capable of AirPrint or IPP Everywhere, which means they don't need to be installed to work - the device is found by Avahi and the print capabilities are communicated via IPP protocol - they are basically driverless devices. There are two solutions in Fedora which implement IPP everywhere:

• CUPS 'everywhere' model
• cups-filters 'driverless' driver

CUPS 'everywhere' model

It is CUPS implementation of IPP everywhere standard, available as a special printer model. The model is used when you use CUPS temporary queue for your device or if you install your device with as IPP Everywhere model in CUPS web ui or via lpadmin (using -m everywhere).

Because the created PPD file depends on IPP communication with printer, we need info which is gathered from the device. You can use ipptool for that:

$ ipptool -tv <your_printer_device_uri> get-printer-attributes.test &> ipptool_log

Attach the created ipptool_log to the bugzilla ticket if needed.

cups-filters 'driverless' driver

Cups-filters special driver which is used for generating PPD according IPP Everywhere standard. The driver is used if you choose driverless model during printer installation.

We need get-printer-attributes request output too:

$ ipptool -tv <your_printer_device_uri> get-printer-attributes.test &> ipptool_log

and debug logs from the driver itself when it generates PPD for your device:

$ driverless -d cat <ipp_device_uri> 2> driverless_debug > created_ppd

Attach all created files to the bugzilla ticket if needed.

Finding where the problem lies

When a print job is processed it is sent through a chain of filters to convert the file into a format the printer can understand, and then finally sent to a backend, a program which can transport the data to the printer. By slightly changing how you print you can try a different printing path to see if that changes anything. If it works around the problem, you know which area the problem was in -- include that information in a bug report so that we can fix it.

Application

Try printing from a different application to see if the problem goes away or if it occurs regardless of how a file is printed. Try printing the document from the command line using the lp command.

Document format

If you are having problems printing PDF files, try printing other types of file to see if the problem is with printing anything or if it is specific to printing PDF files. Try converting the file to a different format and printing that.

If the problem relates to printing text files, try removing/installing the paps package. This package provides an alternative text-to-PostScript filter to the one that comes with CUPS.

To inspect the document that was submitted to CUPS for printing, enable the PreserveJobFiles option like this:

cupsctl PreserveJobFiles=yes

Submitted job documents will remain in /var/spool/cups. There are files with two types of names - dXXXXX-YYY and cXXXXX. dXXXXX-YYY is file which goes to CUPS system, unfiltered file - XXXXX is job ID, which is filled with zeros to be 5 characters long, and YYY is sequence number of file in the job. cXXXXX is file which contains printing options for a job specified by job ID in XXXXX. Please attach dXXXXX-YYY to the bug for a job when you experience the issue

Running filters by hand

More advanced users may like to try running the CUPS filters by hand and examining the data file at each step as it is converted between different formats. Here is an example of doing this for a gutenprint queue named pqueue with the CUPS test page which is its own special MIME type, application/vnd.cups-banner:

First you need to know the filter pipeline for application/vnd.cups-banner --> printer/pqueue (output MIME type). You can either enable debugging, print a test page, look into /var/log/cups/error_log and you'll find something similar to:

envp[29]="FINAL_CONTENT_TYPE=printer/pqueue"
Started filter /usr/lib/cups/filter/bannertopdf (PID 1111)
Started filter /usr/lib/cups/filter/pdftopdf (PID 1112)
Started filter /usr/lib/cups/filter/gstoraster (PID 1113)
Started filter /usr/lib/cups/filter/rastertogutenprint.5.2 (PID 1114)

or run

/usr/lib/cups/filter/bannertopdf 1 me '' 1 '' </usr/share/cups/data/testprint >bannertopdf.pdf
cupsfilter -e -m printer/pqueue -p /etc/cups/ppd/pqueue.ppd bannertopdf.pdf > /dev/null

and you'll see:

INFO: pdftopdf (PID 1111) started.
INFO: gstoraster (PID 1112) started.
INFO: rastertogutenprint.5.2 (PID 1113) started.

note:
This filter pipeline is from cups-1.6. With cups < 1.6 you can see bannertops -> pstops -> pstoraster instead.

Now you can run filters by hand:

export PPD=/etc/cups/ppd/pqueue.ppd
/usr/lib/cups/filter/bannertopdf 1 me '' 1 '' </usr/share/cups/data/testprint >bannertopdf.pdf
/usr/lib/cups/filter/pdftopdf 1 me '' 1 '' <bannertopdf.pdf >pdftopdf.pdf
/usr/lib/cups/filter/pdftoraster 1 me '' 1 ''<pdftopdf.pdf >out.ras
/usr/lib/cups/filter/rastertogutenprint.5.2 1 me '' 1 ''<out.ras >out.prn

Here, evince or okular can be used to examine the output after the first two filters, rasterview can be used to examine the output of the third filter, and the last filter's output must be inspected by hand or sent directly (lpr -oraw out.prn) to the printer.

Driver

If you have access to a different make/model of printer it might be worth trying to see if the problem occurs on both of them or just one. This can give an indication about whether it is a problem with a particular driver, or if it is a more general problem.

Even if you only have access to the one printer there is often a choice of drivers to use for a given printer model, and trying each one in turn can be useful in narrowing down the problem. See above for how to do that.

Foomatic

For Foomatic drivers you can try enabling Foomatic debugging by editing the file /etc/foomatic/filter.conf and adding a line:

debug: 1

Next time you print a job to a queue using foomatic the debugging will be put in /tmp/foomatic-rip.log, and the input file as received by foomatic-rip will be in /tmp/foomatic-rip.ps.

Backend (job transport)

It may be possible for you to try a different backend. Using system-config-printer, double-click on the printer queue icon and click the Change... button next to the Device URI field. You may see a Connection expander arrow near the bottom right hand corner of the window -- click that to see which backends are available. For USB-connected HP printers, typically either of the hp and usb backends can be used.

For capturing USB communication:

• find out the bus number where USB device is connected, f.e.:

$ lsusb
Bus 002 Device 010: ID 03f0:012a HP, Inc HP LaserJet M1536dnf MFP
      =

• start USB packet capture:

$ sudo tcpdump -i usbmonN -s0 -w usb.pcap

where N is the bus number.

For network printers you may have different protocols you can try.

• socket is for HP JetDirect (usually port 9100)
• lpd is for older style UNIX print shares
• smb is for CIFS shares from Windows systems
• ipp is for Internet Printing Protocol-enabled devices and also for other CUPS servers
  • You can capture the IPP traffic with tcpdump like this (the interface name may differ from p4p1):

 tcpdump -n -i p4p1 -U -s0 -w ipp.pcap port ipp

• bjnp is for Canon's proprietary bjnp network protocol (usually port 8611)

Configuration tool

If your problem relates to configuring print queues, try using one of the other methods of doing so. There are four available:

• The GNOME 3 System Settings application (control-center), System Settings > Printers from the GNOME Shell
• system-config-printer, System > Administration > Printing from the GNOME menu
• the CUPS web interface, http://localhost:631/
• the command line tools lpadmin, lpoptions, cupsctl, cupsaccept, cupsenable etc.

User stories

There are several common user stories when it comes to debugging printing issues. I'll mention some of them with steps how to get necessary information.

I have HP printer and have a problem with HPLIP script

Please follow the steps in the following sections:

• enable CUPS debug logging
• start to capture journal logs
• run the script with enabled debugging
• get the journal logs
• attach the files to the bugzilla ticket and turn off debug logging
• provide printer model name and printer PPD file from /etc/cups/ppd/

I have HP printer, installed it with HPLIP and have a problem with it

HPLIP installed print queue has a device uri starting with hp://.

Please follow the steps in the following sections:

• enable CUPS debug logging
• start to capture journal logs
• trigger your issue
• get the journal logs
• attach the requested files to the bugzilla ticket and turn off debug logging
• provide printer model name and printer PPD file from /etc/cups/ppd/

My printer doesn't print correctly or at all, but I can see the printer in print dialog

Please follow the steps in the following sections:

• enable CUPS debug logging
• prepare CUPS for job logging
• restart CUPS service
• trigger your issue - print the specific document to the specific print queue you have problem with
• get the job log for the job you have just triggered
• attach the created files to the ticket and turn off debugging
• attach your printer PPD file from /etc/cups/ppd/ if available
• attach the file you wanted to print
• tell what application you printed from
• mention your printer model

CUPS generic issue

For generic issues - printer wasn't found, segfault - please follow the steps in the following sections (avahi-daemon must run):

• enable CUPS debug logging
• start to capture logs
• trigger the issue - e.g. try to find printers via sudo lpinfo -l -v, do some action in web ui - depends on your problem
• get the logs
• attach created files to the ticket and turn off debugging
• put the output of lpinfo into a file and attach it
• put the output of both lpstat commands into a file and attach it

My printer doesn't print correctly - I use 'everywhere' model

Please follow the steps in the following sections:

• get data from get-printer-attributes request
• follow the steps with CUPS job log user story

I have a generic problem with cups-browsed

Please follow the steps in the following sections:

• enable CUPS debug logging
• enable cups-browsed logging, but don't restart cups-browsed yet.
• start to capture cupsd logs
• start cups-browsed via systemctl and start to capture its logs:

$ journalctl -u cups-browsed -f > cups_browsed_log

• trigger the issue or wait until cups-browsed triggers the issue itself
• cancel cups-browsed and cupsd log captures
• attach created files cups_whole_log and cups_browsed_log to the ticket and turn off debugging

Printer found by cups-browsed doesn't print or print badly

The most difficult user story - we need to know how the print queue was created and how it behaves during printing. The print queue found by cups-browsed has a device uri starting with implicitclass://.

Please follow the steps:

• get printer info from get-printer-attributes and PPD file
• enable CUPS debug logging
• enable cups-browsed logging, but don't restart cups-browsed yet.
• start to capture cupsd logs
• start cups-browsed via systemctl and start to capture its logs:

$ journalctl -u cups-browsed -f > cups_browsed_queue_creation

• give cups-browsed some time to process found devices (depends on how many devices you have in the local network or how many print queues are stored in the location you set with BrowsePoll directive)
• cancel cups-browsed and cupsd log captures - save the files as cups_queue_creation and cups_browsed_queue_creation

Now we need to capture the logs during printing:

• prepare CUPS for job logging
• restart CUPS service
• start to capture cups_browsed logs again:

$ journalctl -u cups-browsed -f > cups_browsed_printing

• trigger your issue - print the specific document to the specific print queue you have problem with
• get the job log for the job you have just triggered and cancel the capture of cups-browsed logging
• attach all gathered log files

Filing a bug report

Deciding which component

Problems involving printing may relate to several components.

The configuration GUI (See above) is either GNOME 3 System Settings application or system-config-printer. These packages also provide the printer applet, handle automatic queue creation, and disable/enable queues when USB printers are disconnected and reconnected.

Most GTK+ applications use the GTK+ print dialog. If the problem occurs when using GTK+ applications but not when printing from the command line or from another non-GTK+ application, the problem should probably be reported against gtk2. If the problem occurs with only one GTK+ application, and other GTK+ applications print fine, the bug should be filed against that particular application.

If the problem only happens with PDF files, the bug may well be in poppler (the CUPS pdftops filter is a wrapper around one of the poppler utility programs).

Report bugs only seen using the smb backend against samba.

For bugs only seen when using the hp backend, or the hpijs or hpcups drivers, select hplip for the component.

For bugs for cups-browsed daemon and its printer discovery, please select cups-filters

Other possibilities, depending on the problem, include:

• foomatic (the Foomatic CUPS filter and driver)
• foomatic-db (the actual printer database used by Foomatic)
• ghostscript (which converts PostScript to other formats)
• gutenprint (a driver that supports very many printers)

For anything else, or if you are not sure, choose cups or use your best guess.

Other information to include

Be prepared to include some information about your system as well. Some of this can be gathered automatically using the printing troubleshooter, but you may also need to include other information.

Before gathering of information

• Please change your OS locale to English. Manual [1].
• Please attach gathered information as archive (example is here, you may need root permissions) to the bugzilla issue.
• Please do not forget to trigger your issue after debug enabling and restarting cups and before information gathering.

Information to gather

• the PPD file for the print queue (from the /etc/cups/ppd directory)
• the document you are attempting to print -- if the document is large, please try to see if the problem also occurs with a smaller document
• cupsd journal logs when debug level 2 is turned on. How-to for turning debug2 on and for getting logs from systemd-journald is above.
• if the issue is connected to a print job, attach journal logs for this specific job too. How-to get logs here, example with JID. You can find out JID value by command:

$ lpstat -W all

. Find your job there and JID is a number after '-'.

• If the issue is about f.e. 'printing from evince prints garbage, but printing from libreoffice works', then attach two separate files - first will contain logs when you print from evince, latter logs when you print from libreoffice.
• troubleshoot.txt from system-config-printer (BEWARE: it doesn't contain journal logs - don't forget to attach them too).
• make and model of printer
• config files - /etc/cups/client.conf (if it contains any changes from default), /etc/cups/cupsd.conf
• if the issue is with cups-browsed and printer's discovery, attach /etc/cups/cups-browsed.conf and cups-browsed logs gained by how-to above.

Some example documents can be found in the Printing Test Cases category.

Further reading

The main printing page has more information about how printing works in Fedora.

How to debug scanning issues

SANE library, communication libraries and backends can turn on and off debug logging via SANE_DEBUG_* environment variables.

The common environment variables:

• SANE_DEBUG_DLL - enables debugging SANE library
• SANE_DEBUG_SANEI_USB - enables debugging communication library for USB - add the environment variable if your device is connected via USB cable
• SANE_DEBUG_SANEI_TCP - enables debugging communication library for wireless/ethernet - add the environment variable if your device is connected by Wifi or Ethernet

Environment variables for enabling debugging a specific backends have a structure - SANE_DEBUG_<backend_name>, so the environment variable for f.e. HPAIO backend is SANE_DEBUG_HPAIO.

You can find which SANE backend supports your device here. If your device is HP and it isn't supported by airscan backend or any other SANE backend, it can be supported by hpaio backend from hplip package, see the list of supported devices here.

Before you start debugging

The acquired log files can be quite big in case you use high resolution, do colored scanning, use higher scanning steps etc., so it would be great if you checked whether your issue happens:

• with the lowest scanning step
• with the lowest resolution
• in Lineart mode
• with .pnm as output file format

If the issue happens even with the lowest settings, do use these settings during debugging steps below.

Debugging scanner discovery

If you don't see your scanner in scanning application, then debugging of discovery process is in order. I prefer using scanimage in the examples, but the similar steps can be applied for every scanning application like xsane, scanadf, simple-scan etc.

You will need to use environment variables when you start a scanning application (scanimage in this case). The environment variables used with scanimage command depends on how your scanner is connected and which backend suppose to support it. So for getting debug logs there is a skeleton:

$ SANE_DEBUG_DLL=255 SANE_DEBUG_<backend>=255 SANE_DEBUG_SANEI_<connection>=255 scanimage -L &> discovery_output

where <backend> is the name of backend which supports your device in capitals (f.e. PIXMA, AIRSCAN, GENESYS, HPAIO). You can find which backend supports your device here. If your device isn't on the list and you were able to scan in the past or you know your device supports eSCL or WSD, use AIRSCAN. <connection> depends on how your device is connected - strings are TCP or USB.

Please attach the created discovery_output file as an attachment to the bugzilla ticket. If the file is too big (let's say over 5MB), do follow the steps for dividing the logs.

Debugging scanning process

If the scanner is found, but an issue happens during scanning itself, we need to debug scanning process itself - which means debugging communication between backend and scanner when you start scanning a document.

The debugging scanning itself looks similar as discovery - setup the environment variables before running the command/scanning application and catch logs into a file. The command's skeleton is (if you use xsane):

$ SANE_DEBUG_DLL=255 SANE_DEBUG_<backend>=255 SANE_DEBUG_SANEI_<connection>=255 xsane &> debug_log

or (once you find out device uri from scanimage -L - see the previous section):

$ SANE_DEBUG_DLL=255 SANE_DEBUG_<backend>=255 SANE_DEBUG_SANEI_<connection>=255 scanimage -d <device_uri> > out.pnm 2> debug_log

, where you substitute <device_uri> for the actual device uri, f.e. 'hpaio:/net/laserjet_m1536dnf_mfp?ip=192.168.1.112'.

<backend> is the name of backend which supports your device in capitals (f.e. PIXMA, AIRSCAN, GENESYS, HPAIO). You can find which backend supports your device here. If your device isn't on the list and you were able to scan in the past or you know your device supports eSCL or WSD, use AIRSCAN. <connection> depends on how your device is connected - strings are TCP or USB.

Please attach the created file - debug_log - as an attachment to the bugzilla ticket. If the file is too big (let's say over 5MB), do follow the steps for dividing the logs.

Getting a scanner device uri

This point is basically a manual how to get a scanner uri for debugging scanning itself via scanimage. You don't need to provide a scanner uri in GUI applications like xsane or simple-scan, because the application will do it for you or you can choose the scanner by a mouse click.

The scanimage -L command returns an output where device uri of the device is shown, f.e.:

$ scanimage -L
device `v4l:/dev/video0' is a Noname Integrated Camera: Integrated C virtual device
device `hpaio:/net/laserjet_m1536dnf_mfp?ip=192.168.1.112&queue=false' is a Hewlett-Packard laserjet_m1536dnf_mfp all-in-one

F.e.the string 'hpaio:/net/laserjet_m1536dnf_mfp?ip=192.168.1.112&queue=false' is a device uri for for Hewlett-Packard laserjet_m1536dnf_mfp all-in-one scanner.

Debugging HP scanner if it is supported by HPLIP

The hplip package doesn't have unified logging, so some logs come out of HPAIO backend to standard output and HP internal utilities logs come to journal. So we need to capture both to get the understanding of situation.

It can be done this way:

• start capturing journal logs at background:

$ journalctl -f > journal_logs &

• trigger an action (discovery or scanning)

• kill the journalctl process, f.e. this way (if there is only one journactl process)

$ kill `pidof journalctl`

then attach the created file - journal_logs - as an attachment to the bugzilla ticket. Please do only one action per capture - that means if you are asked to attach log files for HP scanner discovery and scanning supported by hplip, you will attach as an attachment four files - discovery_output, journal_logs for discovery output, debug_logs and journal_logs for debug_logs.

Debugging sane-airscan

If your device supports eSCL or WSD (you can find it out from device specification - look for the mentioned protocols or AirScan), then its scanning functionality is supported by sane-airscan. Regarding debugging, on the top of usual logging sane-airscan gathers a communication dump and output image, which is helpful during investigation.

sane-airscan debugging can be enabled in /etc/sane.d/airscan.conf by setting:

[debug]
trace = /path/to/dir/where/debugfiles/will/be/saved
enable = true

Then do trigger your issue (discovery or scanning), go to the dir you defined in /etc/sane.d/airscan.conf, take all files from there and attach them to the bug ticket.

How to divide the logs

In case your debug log is too big for bugzilla to attach (because your issue doesn't happen with the lowest settings or logs are big even with the lowest settings), do divide the logs to three files like this:

$ grep dll debug_log > debug_log_dll
$ grep <connection> debug_log > debug_log_connection
$ grep <backend> debug_log > debug_log_backend

<backend> is the name of backend which supports your scanner (pixma, genesys, plustek, hpaio, airscan etc.), <connection> is the type of connection you use for the device (tcp, usb).

The division makes the investigation more difficult (the person needs to have three opened files at the same time), so do divide the logs only if log file is too big.

Known issues

Here are several known issues, which arise with certain circumstances, and there isn't general solution or upstream didn't want to add the solution to its project:

cups-browsed

Cannot print due 'No destination hostname provided by cups-browsed, is it running?'

cups-browsed sometimes loses connection to print server (usually with old ones, like cups-1.4.2) when laptop changes network connection (change of WiFi network or after hibernate/suspend). You can make printing working again with cancelling your jobs and restarting cups-browsed by

$ cancel -a
$ sudo systemctl restart cups-browsed

cups-browsed consumes large amount of CPU

Creating local printer queues takes long time for some printers with larger PPD file, so timeout of http connection will time out and it creates infinite loop of creating local printer queues. To solve this issue, please add

HttpLocalTimeout N
HttpRemoteTimeout N

into /etc/cups/cups-browsed.conf, where 'N' is number of seconds after which connection is timed out. Then restart cups-browsed service. This option is currently in Fedora 27 and above.

[SINCE FEDORA 27] cups-browsed creates different printer queue names than before

This issue is connected to remote cups queues, which are advertised by older CUPS version (usually below cups-1.5, e.g. RHEL 6). Cups-browsed creates local print queues named by printer's DNS-SD ID by default and naming by remote cups queue is enabled again by adding:

LocalQueueNamingRemoteCUPS RemoteName

into /etc/cups/cups-browsed.conf and restart cups-browsed service.

Remote DNS-SD-advertised CUPS queue shredder on host barn.local is raw, ignored.

Server queues don't appear in desktops.

jourcnalctl -u cups-browsed output shows:

Network interfaces: lo (127.0.0.1, localhost), eno1 (172.16.0.123, desk.example.com, 172
Avahi Resolver: Service 'HP LaserJet 4100 Series @ barn' of type '_ipps._tcp' in domain.....
Avahi-Resolver: Instance: HP LaserJet 4100 Series
Found CUPS queue/class: shredder on host barn.local.
Remote DNS-SD-advertised CUPS queue shredder on host barn.local is raw, ignored.
listening

# Set CreateRemoteRawPrinterQueues to "Yes" to let cups-browsed also
# create local queues pointing to remote raw CUPS queues. Normally,
# only queues pointing to remote queues with PPD/driver are created
# as we do not use drivers on the client side, but in some cases
# accessing a remote raw queue can make sense, for example if the
# queue forwards the jobs by a special backend like Tea4CUPS.

CreateRemoteRawPrinterQueues Yes

uncommenting / switching to Yes in /etc/cups/cups-brosed.conf solves the issue.

cups-filters

Printing takes a long time or doesn't print at all

When your printer needs a lot of time to do printing (from your POV) or doesn't print at all (some Xerox printers have such problems with gs renderer, so they are working again only with pdftops renderer), you can try to change the default postscript renderer. The default renderer in Fedora for most printers is gs filter from Ghostscript, but we have pdftops filter from Poppler for Brother, Minolta and Konica Minolta printers - this setup is called hybrid.

Other available renderer setups are gs (from Ghostscript), pdftops and pdftocairo (from Poppler), mupdf (from mupdf) and acroread (from adobe reader, not in Fedora official repositories), then you can set different default renderer for your print queue like this:

# lpadmin -p <printer-name> -o pdftops-renderer-default=gs/pdftops/pdftocairo/mudpf/acroread/hybrid

BEWARE: Most 'slow' printing issues are caused by PDF creating applications, which generates bad PDF file - and that bad generated PDF file is mostly the core of problem. To sum it up, slow printing issue can rise again with different PDF file, then it is on user's decision: if he wants to print fast and probably sometimes change the default renderer, or slow printing is not such critical issue.

CUPS

[Fixed in F33 and later] Firefox, Evince (PDF viewer), GVim, Gedit, Gnome Control Center show a 'dummy'/duplicate print queue, which doesn't work

This bug is connected to every application which uses GTK print dialog. GTK dialog decided to take information about available from two sources - mDNS messages from Avahi and CUPS - this dummy/duplicate print queue is a print queue GTK created in its dialog based on Avahi messages, but it doesn't exist in CUPS, because no one created it, and later GTK behaves like it exists in CUPS. So every time an user wants to print, GTK sends a request to CUPS for this queue, but it gets dropped by CUPS because the queue doesn't exist.

The feature which GTK is trying to do here is called CUPS temporary queues - GTK developers is currently working on a immediate fix in this bugzilla. The future plan is to use cpdb-backend-cups backend in GTK, but right now we are focusing on the intermediate fix.

CUPS doesn't take nicely some kinds of FQDN

CUPS sometimes has problems with some kinds of FQDN - that means when you use FQDN in 'BrowsePoll' directive in /etc/cups/cups-browsed.conf, CUPS doesn't recognize it as valid hostname - it is solved by adding:

ServerAlias your.own.fully.qualified.hostname.com

into /etc/cups/client.conf and restarting cups service.

[F33+] Printing via IPPS doesn't work

Fedora 33 came up with a raised bar regarding crypto-policies, so SSL and older TLS protocols are disabled on system level. The change breaks printing via IPPS to devices which don't support newer protocols. You can set back legacy crypto support in crypto-policies via:

$ sudo update-crypto-policies --set DEFAULT:FEDORA32

The policy change transitionally has an impact on devices found by cups-browsed, because the daemon prefers IPPS uris if they are reported as available by printer/server.

HPLIP

First I would like to mention that we are not responsible for support HPLIP, which is downloaded and installed from HP website. Please install hplip rpms from official Fedora repositories at most cases.

Hp-plugin: file does not match its checksum. File may have been corrupted or altered

This common error is mostly caused by external causes (server outage, network outage), when wget tries to download plugin, but it returns only error message. It is connected with message:

Plugin download failed with error code = N

where N is return value of wget (man wget), which is used for downloading proprietary plugin. Solutions for this issue may vary - you can wait until servers go up again or try to install plugin, which you download manually from http://www.openprinting.org/download/printdriver/auxfiles/HP/plugins/ (select "Select and install an existing local copy of the plug-in file" during hp-setup or hp-plugin).

Unable to load cupsext

This error can occur when hplip is installed from HP website, or its dependencies are mixed python2 and python3 packages or installed by pip. This is solved by removing all hplip packages (hplip, hplip-gui, hplip-libs, hplip-common, libsane-hpiao) and installing them again all from repositories.

Missing hplip-gui

GUI tools and GUI parts of HP commands are moved to hplip-gui subpackage, because the main package can work without GUI, so the main package is smaller. The outcome of this decision is HP commands need to be run with '-i' option for interactive mode, or hplip-gui subpackage needs to be installed.

Tools, which need to be run with '-i' option for CLI or need to have hplip-gui installed for GUI:

hp-align
hp-clean
hp-colorcal
hp-diagnose_queues
hp-fab
hp-firmware
hp-info
hp-plugin
hp-sendfax
hp-setup
hp-testpage
hp-unload

Tools, which are in hplip-gui:

hp-check
hp-print
hp-systray
hp-toolbox
hp-devicesettings
hp-faxsetup
hp-linefeedcal
hp-makecopies
hp-printsettings
hp-wificonfig

HP printer isn't discovered, doesn't print or doesn't print well

Some HP printers don't work well with URIs provided by CUPS (dnssd, usb, ipp) or they need proprietary plugin from HP, which cannot be in Fedora because of licensing issues. For such printers please try to run:

hp-setup -i -g

for interactive mode, or:

hp-setup -g

for graphic mode. This command installs HP printers and HP scanners. If you have issue about HP printer/HP scanner, which isn't discovered, doesn't print or doesn't print well, please try to install it by 'hp-setup', if it helps. If it doesn't help, please file a bugzilla, attach output of hp-setup and mention that you tried 'hp-setup'.

Device which needs plugin does not work after HPLIP update

Devices which need plugin can stop to work after update to newer HPLIP version - it is due the check for plugin version in the code. The check is necessary to prevent inconsitencies when new features in open sourced HPLIP need new proprietary libraries from plugin. To make your printer work again, just download and install plugin again with:

$ hp-plugin -i

Devices which require a binary plugin stopped to work on Fedora Silverblue/CoreOS

Devices which require a HP close source binary plugin need to have plugin installed every time you start/restart your PC by default. HP closed source script installs the plugins into a readonly directories, so the plugins are removed once you start/restart Fedora. The workaround is to try if your device supports driverless printing and scanning, try hplip-plugin package from RPMFusion or keep installing the plugin everytime you want to print.

HP USB printer/scanner doesn't work due a conflict on USB port

HPLIP proprietary binary plugins tends to conflict on the USB port where HP device is connected, if the HP device is capable of using IPP over USB and if ipp-usb package is installed. The solution is to remove hplip and have the device being maintained by ipp-usb and sane-airscan, because it provides newer open sourced protocols and you are not limited by problems caused by closed source plugins (needed to be reinstalled every time there is a new HPLIP version, they don't work stable on Silverblue/CoreOS).

Terminology for printing and scanning

Printing

Print queue

Abstraction unit in CUPS for a printer - it has a device uri, which represents connection to the device, and can exist with classic driver (PPD file from different package) or without (driverless printing). The entries you see in print dialogs and settings are those print queues. They can be permanent or temporary.

Permanent print queues

The queues with classic driver or driverless print queue which need to be shared further down the network.

Temporary print queues

The queue which don't need to be installed at all - they show up during print dialog and they disappear once the printing is done successfully. They rely on driverless printing.

Remote CUPS queue

The queue on the different machine, where other cupsd process is running, than on the local machine. They are usually found in enterprise solutions, where printers aren't in the same network as users or if admin wants a centralized monitoring above all printers. In such solutions, users set up cups-browsed to install remote CUPS queue as local queues via BrowsePoll directive, or install a specific queue via GNOME. There can be a solution how to redirect mDNS messages which CUPS server advertises to the networks with users, but I haven't been to setup this correctly yet.

Classic drivers

Those are the binaries and PPD files, which need to be installed for the device to work. This is older way of supporting devices, which will go away in the future.

Driverless printing (wireless/ethernet)

Most of modern devices (2010+) complies to AirPrint, Mopria or IPP Everywhere standard, which means they don't need a classic driver for being able to print. Those devices have IPP (Internet Printing Protocol) 2.0+ implemented within, are capable to 'advertise' themselves via mDNS and they support document formats like PDF, PCLm, JPEG, Apple Raster or PWG Raster.

There are several prerequitises which need to fulfill in OS to have an access to the driverless feature:

• avahi-daemon must run
• there needs to be a '.local' address resolver active - systemd-resolved or nss-mdns
• the device itself must have IPP port (631) and Bonjour/MDNS enabled
• IPP and MDNS need to be enabled in firewall

How does the driverless printing work under the roof (put it simply):

• CUPS sees the printer in mDNS messages via Avahi
• CUPS will find out the printer capabilities via IPP
• if there is a print job, CUPS will set up the filter chain to convert the incoming file into document format which printer understands (Apple Raster, PDF, PWG Raster, PCLm, JPEG)

In case it is needed, PPD file is generated by PPD generator in CUPS or by driverless binary.

One of the features which use driverless printing is CUPS temporary queues.

See manual how to check if your printer is capable of driverless printing.

Printing using a driver

This printing is similar to driverless printing in matter of setting up a filter chain, but:

• it can use limited mDNS and IPP functionality or it doesn't use them at all
• all information about device capabilities is taken from PPD (Postscript Printer Description) file
• can use a specialized filters and specialized communication with the device (depends on driver)

The downsides of this approach is to rely on 3rd party drivers, you need to always install a permanent queue for it and it will go away in the future.

Printing raw data

No filters are started during this printing, the data are sent as they are to the target. This approach is usually used for printing to label printers, or, in the past, for printing to remote CUPS queue. The same as classic drivers, this solution is deprecated and it will be removed in the future.

Printer applications

The binaries which provide support for older devices which aren't capable of complying to driverless standards. The core idea is they will be capable of accepting the old driver and then advertise itself as a device capable of driverless printing. Then the new CUPS will be able to see them and user will be able to print via them as if they were temporary queues. The currently available printer applications in Fedora are ippeveprinter (a part of CUPS - see cups-printerapp package) and lprint (provides support for devices which requires raw printing - mostly label printers). I'm planning to package PAPPL, the library for creating printer applications, and ps-printer-app, a printer application for printers which support Postscript.

Driverless printing (USB)

Driverless printing has its variant for devices which are connected via USB - it is covered by 'IPP over USB' standard. For make it work, you need 'ipp-usb' package, which will register the device with Avahi on localhost - then USB device will look as a wireless/ethernet device. The discovery/printing looks the same as with a wireless/ethernet device with driverless support.

See manual how to check for IPP-over-USB.

Scanning

Classic scanning (via hplip and sane-backends)

The classic scanning works via backends, which are binaries for communication with device. There are several backends, usually created by reverse engineering communication between scanner and MS Windows driver. None of classic backends implements a protocol, which is compatible with most devices available.

Driverless scanning

The driverless scanning uses sane-escl (not built in Fedora) and sane-airscan backends for communicating with newer devices. Those newer devices usually support eSCL (based on AirScan protocol by Apple) or WSD (Web Services for Devices by Microsoft), which sane-airscan is able to use.

Regarding USB scanning, it has the same requirement as printing. The device must support IPP over USB and 'ipp-usb' package must be installed to get driverless scanning via USB.

Useful tricks

How to find out whether my printer is capable of driverless printing?

• look for AirPrint among device specification
• Officially certified printers for IPP Everywhere
• check manual for enabling CUPS temporary queues - if your printer is seen in the end in CUPS commands that way, your printer is capable of driverless printing
• [USB devices only] check for IPP over USB (manual here).

How to find out my multifunction device or standalone scanner is capable of driverless scanning?

• check the device specification and look for eSCL/AirScan/WSD - if any of these are mentioned, the device is capable of driverless scanning
• most devices which advertise they can do AirPrint are capable of AirScan too
• [USB devices only] check for IPP over USB (manual here).

How to find out if my USB device supports IPP over USB

Check whether your USB device has a following text in lsusb -v output:

...
      bInterfaceClass         7 Printer
      bInterfaceSubClass      1 Printer
      bInterfaceProtocol      4 
      iInterface              0 
...

If the device has the bInterfaceClass 7, bInterfaceSubClass 1 and bInterfaceProtocol 4 in the sequence, it supports IPP over USB which is critical for USB device driverless printing and scanning.

How to install a print queue

The answer is you don't have to install at all :) if your device is new enough, is in your local network or is an USB device, has IPP/AirPrint/mDNS enabled and your avahi-daemon is running, CUPS is able to create a temporary queue for you right away in the print dialog, print via it and remove it after successful printing. But there are still use cases when permanent installation is needed like sharing a print queue, different print queue defaults or printer being in different subnet, so I will cover a permanent instalation too.

How to setup CUPS temporary queues with network printer

If your printer is capable of AirPrint, IPP and MDNS is enabled in your printer and printer , then to get CUPS temporary queues working you need:

• have avahi-daemon running:

$ sudo systemctl start avahi-daemon

• have cups.socket enabled and running running:

$ sudo systemctl enable cups.socket
$ sudo systemctl start cups.socket

• enable IPP and MDNS in your firewall settings

After this the temporary queue will appear in the print dialog and you don't need to install a specific print queue unless you have a reason for it.

You can check if your printer is seen in mDNS messages by (avahi-tools must be installed):

$ avahi-browse -avrt
...
= enp0s25 IPv4 HP LaserJet M1536dnf MFP (42307C)             _ipp._tcp            local
   hostname = [NPI42307C.local]
   address = [192.168.1.10]
   port = [631]
   txt = ["UUID=434e4239-4243-4a42-5859-3c4a9242307c" "Scan=T" "Duplex=T" "Color=F" "note=" "adminurl=http://NPI42307C.local." "priority=10" "product=(HP LaserJet M1536dnf MFP)" "ty=HP LaserJet M1536dnf MFP" "URF=CP99,W8,OB10,PQ3-4-5,DM1,IS1-4,MT1-2-3-5,MT1-2-3-5,RS600" "rp=ipp/printer" "pdl=application/postscript,application/vnd.hp-PCL,application/vnd.hp-PCLXL,application/pdf,image/urf" "qtotal=1" "txtvers=1"]
...

and if CUPS or its backends see the printer by commands:

(lists all existing print queues - permanent or temporary)

$ lpstat -e
HP_LaserJet_M1536dnf_MFP_42307C_

or

(lists all devices, which CUPS sees in the local network or USB)

$ lpinfo -l -v
...
Device: uri = ipp://HP%20LaserJet%20M1536dnf%20MFP%20(42307C)._ipp._tcp.local/
        class = network
        info = HP LaserJet M1536dnf MFP (driverless)
        make-and-model = HP LaserJet M1536dnf MFP
        device-id = MFG:HP;MDL:LaserJet M1536dnf MFP;CMD:PDF,PS,PCL,AppleRaster,URF;
        location = 
...

How to setup CUPS temporary queues with USB printer

USB printers have only one additional prerequisite, installing ipp-usb, which will transform IPP over USB devices to network printer on localhost:

$ sudo dnf -y install ipp-usb

Then you can follow the steps in manual for network printers.

How to install a permanent print queue

1) via CUPS web UI

• start cups.service

$ sudo systemctl start cups

• go to localhost:631 in your browser, and select 'Administration' tab
• click on 'Add printer' and follow the dialogs

2) via CLI commands

• you will need a device uri - <device_uri>, f.e.:

$ lpinfo -l -v
...
Device: uri = ipp://HP%20LaserJet%20M1536dnf%20MFP%20(42307C)._ipp._tcp.local/
              ================================================================

and a driver name - <driver>, f.e.:

$ lpinfo -m
....
everywhere IPP Everywhere
==========
...

$ lpadmin -p <name> -v <device_uri> -m <driver> -E

where <device_uri> and <driver> are underscored strings from previous commands and <name> is a print queue name, which is chosen by you.

How to install a scanner

Scanners in Linux don't have to be installed the same way as printers are if they are in the same network or connected via USB - you just need sane-backends to be installed and any scanning application will communicate with scanner/multifunction device via the backend which supports the scanner.

However, the older HP scanners and multifunction devices require an additional package - hplip - and its binary plugins downloaded via hp-plugin -i if they aren't supported by sane-backends already.

How to make driverless scanning to work

For LAN located and USB devices:

• have avahi-daemon enabled and running

$ sudo systemctl enable avahi-daemon
$ sudo systemctl start avahi-daemon

• enable MDNS in firewall
• [USB devices only] install ipp-usb

For network scanners in a different network:

• set the scanner device uri in /etc/sane.d/airscan.conf - see:

man sane-airscan

How to setup mDNS with systemd-resolved

systemd-resolved is enabled and running by default since F33 and can be setup to work with Avahi on mDNS support which CUPS needs - Avahi does the advertising, registering and sharing devices, and resolved will handle '.local' address resolution. It will work with following steps:

• put 'MulticastDNS=resolve' into /etc/systemd/resolved.conf

$ sudo systemctl restart systemd-resolved
$ sudo nmcli connection modify <connection_name> connection.mdns yes connection.llmnr yes
$ sudo systemctl restart NetworkManager

How to compress files

Example:

$ tar -czvf cups-information.tar.gz /etc/cups cups.logs troubleshoot.txt lpinfo.log

Restarting cups service

You restart cups service with:

sudo systemctl restart cups.service