Public bug reported:
Package: cups-daemon
Version: 2.4.7-1.2ubuntu7.14
OS: Ubuntu 24.04 LTS (via Linux Mint 22.3)
Description
-----------
/etc/logrotate.d/cups-daemon does a full CUPS restart in its postrotate
script:
postrotate
invoke-rc.d --quiet cups restart > /dev/null
endscript
When logrotate runs (daily, around midnight) this fully stops and starts
cupsd. The scheduler socket is recreated and cups-browsed re-creates its
queues. Any long-running application that cached the printer list at
startup (or holds an open connection to cupsd) is then left with a stale
reference: the printer disappears from the print dialog or the print
button is grayed out. So printing fails until the application is restarted.
This is easy to hit with long-lived desktop apps, especially if a Flatpak
build is used, which bundles their own CUPS client libraries. It is not
Flatpak-specific, though: any application left running across the nightly
rotation can be affected.
Steps to reproduce
------------------
1. Start an application and open its print dialog; confirm the printer
is listed.
2. Force the CUPS log rotation:
sudo logrotate -f /etc/logrotate.d/cups-daemon
3. Without restarting the application, open the print dialog again.
Expected: the printer is still available and the print button is active.
Actual: the printer is gone or the print button is grayed out - until
the application is restarted.
Suggested fix
-------------
Replace "restart" with "reload" in the postrotate script:
postrotate
invoke-rc.d --quiet cups reload > /dev/null
endscript
"reload" sends SIGHUP, which makes cupsd reopen its log files (the actual
purpose of the postrotate) without tearing down the daemon, its socket,
or the cups-browsed queues, so long-running clients keep working.
** Affects: cups (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2165964
Title:
logrotate restarts cups (instead reloading it) and most programs fail
to print (due to a cached printer list)
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