_restart console command restarts the srcds binary.
_restart does not, however, restart the graphical Source Dedicated Server, as it requires closing the window and reopening it in the Tools menu of Steam.
When given, this command waits 10 seconds before restarting the server. Many errors can occur that continue or cancel the restart. Segmentation faults are a prime example:
_restart PreMinidumpCallback: updating dump comment Looking up breakpad interfaces from steamclient Calling BreakpadMiniDumpSystemInit /srcds/css/css/srcds_run: line 374: 6909 Segmentation fault (core dumped) $HL_CMD cat: hlds.6901.pid: No such file or directory email debug.log to email@example.com Sat Jun 01 00:00:00 CDT 2012: Server restart in 10 seconds
This segmentation fault could have canceled the restart and simply quit the server, but the server continued.
Sometimes the server simply quits instead of restarting for no obvious reason:
_restart Reference Count for Material ___error (10) != 0 Reference Count for Material __depthwrite00 (1) != 0 Reference Count for Material __depthwrite01 (1) != 0 Reference Count for Material __depthwrite10 (1) != 0 Reference Count for Material __depthwrite11 (1) != 0 Reference Count for Material ___glintbuildmaterial (1) != 0 Reference Count for Material __particlesdepthwrite (1) != 0 Sat Jan 01 00:00:00 CDT 2012: Server Quit