Thanks for your answer Rémi but i've found another problem, i reinstall an ubuntu feisty distro and it tells me that the MIT-SHM major opcode is 143 : $ xdpyinfo -ext MIT-SHM|grep MIT-SHM MIT-SHM MIT-SHM version 1.1 opcode: 143, base event: 94, base error: 166 an other friend on ubuntu edgy told me ...