É difícil procurar por esse problema, pois há muitas perguntas sobre reinicialização, bloqueio de tela, etc., mas eu dei uma olhada e não consegui encontrar nada, então aqui vai.
Estou executando o Mint 14 (MATE) com uma configuração relativamente padrão. Não tenho certeza de quais outras informações devo fornecer, mas terei prazer em adicionar detalhes que ajudem na pergunta. Eu uso xscreensaver e desde que eu apenas bloqueie a tela por alguns minutos, isso funciona bem. Se eu estiver longe do meu computador com a tela bloqueada por mais de 10 minutos, é quase garantido que o computador será reinicializado, perdendo tudo que eu tinha aberto. Isso é extremamente frustrante e eu realmente preciso corrigi-lo de alguma forma, mas parece haver muito pouco a ser feito para rastrear esse problema. Eu tentei executar xscreensaver com log detalhado, mas não há nada obviamente errado (aqui estão os últimos 10 minutos antes de uma falha):
xscreensaver: 14:27:07: 1: spawning "flipscreen3d -root" in pid 11972.
glslideshow: unable to load font "-*-helvetica-medium-r-normal-*-180-*", using "fixed"
xscreensaver: 14:30:07: 0: killing pid 11971 (glslideshow)
xscreensaver: 14:30:07: 1: killing pid 11972 (flipscreen3d)
xscreensaver: 14:30:07: 0: visual 0x21 (TrueColor, depth: 24, cmap: 256)
xscreensaver: 14:30:07: 0: saver window is 0x1a00243.
xscreensaver: 14:30:07: 1: child pid 11972 (flipscreen3d) terminated with signal 15.
xscreensaver: 14:30:07: 0: destroyed old saver window 0x1a0023d.
xscreensaver: 14:30:07: 0: spawning "photopile -root -scale 0.6046 -count 9 -duration 3" in pid 15435.
xscreensaver: 14:30:07: 0: child pid 11971 (glslideshow) terminated with signal 15.
xscreensaver: 14:30:07: 1: visual 0x21 (TrueColor, depth: 24, cmap: 256)
xscreensaver: 14:30:07: 1: saver window is 0x1a00245.
xscreensaver: 14:30:07: 1: destroyed old saver window 0x1a0023f.
xscreensaver: 14:30:07: 1: spawning "flipscreen3d -root" in pid 15436.
photopile: font -*-helvetica-bold-r-normal-*-240-* does not exist, using -*-helvetica-bold-r-normal-*-180-*
photopile: font -*-helvetica-bold-r-normal-*-180-* does not exist, using fixed
photopile: unable to load font "-*-helvetica-bold-r-normal-*-240-*", using "-*-helvetica-medium-r-normal-*-240-*"
photopile: unable to load font "-*-helvetica-medium-r-normal-*-240-*", using "-*-helvetica-medium-r-normal-*-180-*"
photopile: unable to load font "-*-helvetica-medium-r-normal-*-180-*", using "fixed"
xscreensaver: 14:33:07: 0: killing pid 15435 (photopile)
xscreensaver: 14:33:07: 1: killing pid 15436 (flipscreen3d)
xscreensaver: 14:33:07: 0: visual 0x21 (TrueColor, depth: 24, cmap: 256)
xscreensaver: 14:33:07: 0: child pid 15435 (photopile) terminated with signal 15.
xscreensaver: 14:33:07: 0: saver window is 0x1a00249.
xscreensaver: 14:33:07: 0: destroyed old saver window 0x1a00243.
xscreensaver: 14:33:07: 0: spawning "photopile -root -scale 0.6046 -count 9 -duration 3" in pid 18945.
xscreensaver: 14:33:07: 1: visual 0x21 (TrueColor, depth: 24, cmap: 256)
xscreensaver: 14:33:07: 1: saver window is 0x1a0024b.
xscreensaver: 14:33:07: 1: child pid 15436 (flipscreen3d) terminated with signal 15.
xscreensaver: 14:33:07: 1: destroyed old saver window 0x1a00245.
xscreensaver: 14:33:07: 1: spawning "photopile -root -scale 0.6046 -count 9 -duration 3" in pid 18946.
photopile: font -*-helvetica-bold-r-normal-*-240-* does not exist, using -*-helvetica-bold-r-normal-*-180-*
photopile: font -*-helvetica-bold-r-normal-*-180-* does not exist, using fixed
photopile: font -*-helvetica-bold-r-normal-*-240-* does not exist, using -*-helvetica-bold-r-normal-*-180-*
photopile: font -*-helvetica-bold-r-normal-*-180-* does not exist, using fixed
photopile: unable to load font "-*-helvetica-bold-r-normal-*-240-*", using "-*-helvetica-medium-r-normal-*-240-*"
photopile: unable to load font "-*-helvetica-bold-r-normal-*-240-*", using "-*-helvetica-medium-r-normal-*-240-*"
photopile: unable to load font "-*-helvetica-medium-r-normal-*-240-*", using "-*-helvetica-medium-r-normal-*-180-*"
photopile: unable to load font "-*-helvetica-medium-r-normal-*-240-*", using "-*-helvetica-medium-r-normal-*-180-*"
photopile: unable to load font "-*-helvetica-medium-r-normal-*-180-*", using "fixed"
photopile: unable to load font "-*-helvetica-medium-r-normal-*-180-*", using "fixed"
xscreensaver: 14:36:07: 0: killing pid 18945 (photopile)
xscreensaver: 14:36:07: 1: killing pid 18946 (photopile)
xscreensaver: 14:36:07: 0: visual 0x21 (TrueColor, depth: 24, cmap: 256)
xscreensaver: 14:36:07: 0: saver window is 0x1a0024f.
xscreensaver: 14:36:07: 0: destroyed old saver window 0x1a00249.
xscreensaver: 14:36:07: 0: spawning "glslideshow -root" in pid 22514.
xscreensaver: 14:36:07: 1: visual 0x21 (TrueColor, depth: 24, cmap: 256)
xscreensaver: 14:36:07: 1: saver window is 0x1a00251.
xscreensaver: 14:36:07: 0: child pid 18945 (photopile) terminated with signal 15.
xscreensaver: 14:36:07: 1: child pid 18946 (photopile) terminated with signal 15.
xscreensaver: 14:36:07: 1: destroyed old saver window 0x1a0024b.
xscreensaver: 14:36:07: 1: spawning "intermomentary -root -num-discs 252" in pid 22515.
glslideshow: unable to load font "-*-helvetica-medium-r-normal-*-180-*", using "fixed"
Eu realmente não espero que alguém saiba exatamente o que está errado baseado apenas nisso, mas algumas dicas sobre como eu deveria tentar rastrear a causa seriam muito apreciadas.