What non-GUI programs (daemons) use glib?
On my Ubuntu system apt-cache rdepends libglib2.0-0 gives me, among many others:
- amanda-server (backup software)
- bitlbee (IRC <-> various IM proxy)
- blktool (tool to tune block device parameters; not a daemon AFAIU)
- collectd (system statistics collection and monitoring daemon)
- consolekit (framework for defining and tracking users, sessions and seats)
- devicekit-disks (abstraction for enumerating block devices)
- devicekit-power (abstraction for power management)
- (I got bored at this point)
This lists package rather than actual binary dependencies; it's possible (but I don't think likely) that some of these packages ship GUI applications that depend on glib.
Let's take, say, consolekit and verify:
dpkg -L consolekit
tells me the daemon is /usr/sbin/console-kit-daemon, and ldd /usr/sbin/console-kit-daemon
tells me it depends on libglib, libgthread, libgmodule, libgobject, libgio, but no GUI stuff. So here you are, a genuine daemon using glib.
I use glib quite a bit in non-GUI programming, especially for FUSE filesystems. Lots of routines to complement glibc, things like hash tables, a linked list implementation, a cross-platform threading library - lots of useful stuff for general-purpose programming. I think of it like C's version of Boost.