Declarative printer configuration fails if printer unavailable

[snicket2100]

Describe the bug

Declarative printer management via hardware.printers.ensurePrinters is a great feature, the problem is that whenever I rebuild my configuration with my network printer not being available (switched off, or me being on a different network), ensure-printers.service fails.

[...]
warning: the following units failed: ensure-printers.service

● ensure-printers.service - Ensure NixOS-configured CUPS printers
   Loaded: loaded (/nix/store/xsigwnz8cxj4hcvkvl8344kxsgdpxfgn-unit-ensure-printers.service/ensure-printers.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Sun 2020-01-26 13:32:19 CET; 19ms ago
  Process: 14791 ExecStart=/nix/store/hkmgwdqx0768gdkilk510zfmx6qd5q1v-unit-script-ensure-printers-start (code=exited, status=1/FAILURE)
 Main PID: 14791 (code=exited, status=1/FAILURE)
       IP: 112B in, 464B out
      CPU: 10ms

Jan 26 13:31:49 xxx systemd[1]: Starting Ensure NixOS-configured CUPS printers...
Jan 26 13:32:19 xxx hkmgwdqx0768gdkilk510zfmx6qd5q1v-unit-script-ensure-printers-start[14791]: lpadmin: Unable to connect to "192.168.111.111:631": Operation now in progress
Jan 26 13:32:19 xxx systemd[1]: ensure-printers.service: Main process exited, code=exited, status=1/FAILURE
Jan 26 13:32:19 xxx systemd[1]: ensure-printers.service: Failed with result 'exit-code'.
Jan 26 13:32:19 xxx systemd[1]: Failed to start Ensure NixOS-configured CUPS printers.
Jan 26 13:32:19 xxx systemd[1]: ensure-printers.service: Consumed 10ms CPU time, received 112B IP traffic, sent 464B IP traffic.
warning: error(s) occurred while switching to the new configuration

A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Add a network printer to hardware.printers.ensurePrinters.
2. Make sure the printer is not available.
3. Run nixos-rebuild.
4. See the error as above.

Expected behavior

It would be nice if ensure-printers.service was able to add/modify printers ignoring network connectivity errors. Unfortunately I couldn't find any option of lpadmin which would allow that :/

Metadata

 - system: `"x86_64-linux"`
 - host os: `Linux 5.4.13, NixOS, 20.03.git.4dbdc31 (Markhor)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.2`
 - channels(root): `"nixos-20.03pre210300.05626cc86b8"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[aanderse]

ping @florianjacob ... though to be honest this sounds like it is working as expected.

[snicket2100]

yeah I agree it is disputable, just that currently it makes declarative printer management nearly impossible on any mobile computers

[florianjacob]

The thing is: My configuration is full of unavailable remote network printers of all sorts, IPP, remote cups, socket, even Canon's proprietary bjnp and everything rebuilds fine. :thinking:

@snicket2100 could you post your full printer & cups config? I guess something is different to mine, which causes your configuration to actually contact the printers on adding them, while mine doesn't.

[snicket2100]

Hmm, it looks like just one IPP printer is enough to trigger this problem for me.

My ensure-printers-start script gets generated as follows:

#! /nix/store/x7hj5hp24flxbx6jnnws5rnjs31g0ybw-bash-4.4-p23/bin/bash -e
/nix/store/7xzpwwsasf0709nm7rs8nzf4jfxsw36k-cups-2.3.0/bin/lpadmin -p 'PRINTERNAME' -E \
   \
   \
  -v 'ipp://1.1.1.2' \
  -m 'everywhere' \
  -o 'PageSize'='A4'
/nix/store/7xzpwwsasf0709nm7rs8nzf4jfxsw36k-cups-2.3.0/bin/lpoptions -d 'PRINTERNAME'

It is the fist command that fails, if I do: /nix/store/7xzpwwsasf0709nm7rs8nzf4jfxsw36k-cups-2.3.0/bin/lpadmin -p 'PRINTERNAME' -E -v 'ipp://1.1.1.2' -m 'everywhere' manually it times out on contacting the printer: lpadmin: Unable to connect to "1.1.1.2:631": Operation now in progress.

I suspect it fails here https://github.com/apple/cups/blob/master/systemv/lpadmin.c#L1216, when called from here https://github.com/apple/cups/blob/master/systemv/lpadmin.c#L630 only for everywhere printers. Not entirely sure that it even has the chance to contact the cups server at that point, but in case it does this is my /etc/cups/cupsd.conf file:

Listen localhost:631

Listen /run/cups/cups.sock

DefaultShared No

Browsing No

WebInterface No

LogLevel info

DefaultAuthType Basic

<Location />
  Order allow,deny
  Allow localhost
</Location>

<Location /admin>
  Order allow,deny
  Allow localhost
</Location>

<Location /admin/conf>
  AuthType Basic
  Require user @SYSTEM
  Order allow,deny
  Allow localhost
</Location>

<Policy default>
  <Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job CUPS-Move-Job>
    Require user @OWNER @SYSTEM
    Order deny,allow
  </Limit>

  <Limit Pause-Printer Resume-Printer Set-Printer-Attributes Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After CUPS-Add-Printer CUPS-Delete-Printer CUPS-Add-Class CUPS-Delete-Class CUPS-Accept-Jobs CUPS-Reject-Jobs CUPS-Set-Default>
    AuthType Basic
    Require user @SYSTEM
    Order deny,allow
  </Limit>

  <Limit Cancel-Job CUPS-Authenticate-Job>
    Require user @OWNER @SYSTEM
    Order deny,allow
  </Limit>

  <Limit All>
    Order deny,allow
  </Limit>
</Policy>

How is that different to your config @florianjacob ?

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[florianjacob]

@snicket2100 Please excuse the enormous delay. The difference between my and your config is indeed that I do not have any IPP Everywhere printer, and your diagnosis seems right hat IPP everywhere printers cannot rebuild when they are offline.

From the current manpage of the lpadmin -m option:

Sets a standard PPD file for the printer from the model directory or using one of the driver interfaces. Use the -m option with the lpinfo(8) command to get a list of supported models. The model "raw" clears any existing PPD file and the model "everywhere" queries the printer referred to by the specified IPP device-uri. Note: Models other than "everywhere" are deprecated and will not be supported in a future version of CUPS.

The “queries the printer referred to by the specified IPP device-uri” specifically sounds like what you have experienced back then already. As the following deprecation note sounds quite concerning and might threaten the NixOS declarative printer configuration, I wanted to ask where you went from there and whether you found a solution that we might are able to integrate for whenever that deprecation notice actually becomes reality.

[tobiasBora]

Note that I also got bitten by this a while ago (so that is part of the reason why I don't use declarative printer management… too bad). In my case I was not using everywhere but a network printer based on dnssd:

  # It works fine, but it always try to reinstall the printer, even if we are not on the network...
  # So it breaks the switch.
hardware.printers.ensureDefaultPrinter = "MyLabPrinter";
hardware.printers.ensurePrinters = [
  {
    name = "MyLabPrinter";
    # Get this from "lpinfo -v" (or use localhost:631 the printers are the good ones)
    deviceUri = "dnssd://25-26%2F103%20MFP%20MyLab%20(color)%20%40%20cups._ipp._tcp.local/cups?uuid=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx";
    # the path should be the the directories below $out/share/cups/model/
    # /nix/store/z0h1jwqw1k8pllkkvgpcqghwsgj1fz3m-hplip-3.19.1/share/cups/model/HP/hp-pagewide_color_e77650-e77660-ps.ppd.gz
    # To get the full list of drivers:
    # lpinfo -m | grep 77660
    # HP/hp-pagewide_color_765-ps.ppd.gz HP PageWide Color E77650-E77660 Postscript
    # HP/hp-pagewide_color_e77650-e77660-ps.ppd.gz HP PageWide Color E77650-E77660 Postscript
    # Only the 'second' driver has stapler enabled.
    model = "HP/hp-pagewide_color_e77650-e77660-ps.ppd.gz";
    location = "Printer_MyLab";
    ppdOptions = {
      PageSize = "A4";
    };
  }
];

Also, if PPD files are going to be deprecated in CUPS, how can we use advanced functionalities not provided by IPP everywhere?

[dpolakovics]

Hello,

i'm not sure if this fits in here, but i noticed the following with an IPP everywhere printer: When i use it with stateless it only works when i restart the service. At boot it becomes a "Local Raw Printer"

Without stateless it always becomes a Local Raw Printer

[zoechi]

For me it failed even when the printer was available.

With just avahi (without hardware.printers.ensurePrinters) the printer was found and working as IPP everywhere (Canon MG3600 series over WiFi).

[rnhmjoj]

At boot it becomes a "Local Raw Printer"

I noticed this as well. With certain printers CUPS seems to be generating a PPD file on-the-fly by querying the printer attributes via IPP, regardless of what "make/model" you have specified.

The solution would probably be to add the printer manually from the web UI, extract the generated PPD file from /var/lib/cups/ppd/ and configure it using lpadmin -P. It seems to work, but I haven't tested actually printing after this.

Note: Models other than "everywhere" are deprecated and will not be supported in a future version of CUPS.

I very much doubt the will do this: it will instantly break support for decades of printers. I can already see people raising their pitchforks.

[IreneKnapp]

this bug definitely went away for a while, or else there are conditions under which it doesn't manifest (perhaps it doesn't break unless the existing CUPS config changes?)

anyway, it's a problem again for me in 24.05, just in case mentioning that is useful to diagnosis or prioritization

[rnhmjoj]

I can confirm that my solution works. So:

1. add the printer manually
2. grab the generated ppd from /var/lib/cups/ppd
3. add the following to your config:

services.printing.enable = true;

services.printing.drivers = lib.singleton (pkgs.linkFarm "drivers" [
  { name = "share/cups/model/myprinter.ppd";
    path = ./myprinter.ppd;
  }
]);

hardware.printers.ensurePrinters = [
  { name        = "my-printer";
    description = "some random printer";
    location    = "at home";
    deviceUri   = "ipps://my-printer.local:631/ipp/print";
    model       = "myprinter.ppd";
  }
];