Configuration options for the x display manager
/etc/X11/xdm/xdm.options contains a set of flags that determine some of the behavior of the X display manager xdm(1x). Most of xdm's behavior is customized through other files; consult the xdm manual page if this manual page does not describe the behavior you want to alter.
/etc/X11/xdm/xdm.options may contain comments, which begin with a hash mark (\(oq#\(cq) and end at the next newline, just like comments in shell scripts. The rest of the file consists of options which are expressed as words separated by hyphens, with only one option per line. Options are enabled by simply placing them in the file; they are disabled by prefixing the option name with \(oqno-\(cq.
Available options are:
Normally, if the nologin(5) file exists, its contents will be displayed using xmessage(1x) (if xmessage is available), and the user will be returned to the xdm login screen after xmessage is dismissed instead of starting the X session. If this option is enabled, xdm starts a session as usual (after xmessage is dismissed, if xmessage is available and the nologin file exists). This behavior is disabled by default: nologin is heeded, not ignored.
Enable this option with caution on \(oqproduction\(cq machines; it causes the daemon to be stopped and restarted on upgrade, even if the process has children (which means it is managing X sessions). Typically when a package that contains a daemon is being installed or upgraded, its maintainer scripts stop a running daemon process before installing the new binary, and restart it after the new binary is installed. Stopping xdm causes immediate termination of any sessions it manages; in some situations this could be an unwelcome surprise (for instance, for remote xdm users who had no idea the administrator was performing system maintenance). On the other hand, for machines that stay up for long periods of time, leaving the old daemon running can be a bad idea if the new version has, for instance, a fix for a security vulnerability (overwriting xdm's executable on the file system has no effect on the copy of xdm in memory). The xdm package's pre-removal script checks to see if the xdm process has any children; if it does, it is possible that someone's session would be killed by stopping xdm, so a warning is issued and an opportunity to abort the upgrade of xdm is provided. Furthermore, restarting xdm on upgrade can be surprising, because a locally-managed X server can change the active VT even while other packages are continuing to upgrade. If, by intent or accident, the X server does not honor the key sequence to switch VTs back to a virtual console, this can be undesirable. This behavior is disabled by default: xdm will be not be stopped or started during an upgrade of its package; the administrator will have to do so by hand (with invoke-rc.d xdm restart or by rebooting the system) before the newly installed xdm binary is used.
Enable this option with caution; it causes the xdm daemon to be started immediately after the package is installed. See the above entry regarding restart-on-upgrade for other caveats regarding the consequences of starting the xdm daemon during package management. This behavior is disabled by default: xdm will not be started when it is installed. Changing this setting can affect future installs if the package is removed, but not purged (which removes \(oqconffiles\(cq, including xdm.options).
This option causes the /etc/X11/xdm/Xreset script to call the sessreg(1x) program to register X sessions managed by xdm in the utmp(5) and wtmp(5) files. If it is disabled, the utmp and wtmp files will have no record of xdm sessions. This behavior is enabled by default; sessreg will be used.
Users of older versions of the Debian system should note that the \(oqrun-xconsole\(cq option has been removed. The shell script named /etc/X11/xdm/Xreset can be edited to disable or modify the running of xconsole on the xdm greeter screen; see xdm(1x) for more information.
Stephen Early, Mark Eichin, and Branden Robinson customized xdm's startup and reset scripts and package maintainer scripts to implement the functionality described above. This manual page was written by Branden Robinson.