Hi Olivier and others,
FS is ext3 so I don't think it's the problem.
Here's the end of the output of 'strace ssh' :
futex(0x7fffc6ce6d0c, FUTEX_WAKE_PRIVATE, 1) = 0
futex(0x7fffc6ce6d0c, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 1, NULL, 7f43905417c0) = -1 EAGAIN (Resource temporarily unavailable)
rt_sigaction(SIGRTMIN, {0x7f438d3d9c60, [], SA_RESTORER|SA_SIGINFO, 0x7f438d3e3710}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0x7f438d3d9cf0, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x7f438d3e3710}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
statfs("/selinux", 0x7fffc6ce6c50) = -1 ENOENT (No such file or directory)
brk(0) = 0x7f43907ba000
brk(0x7f43907db000) = 0x7f43907db000
open("/proc/filesystems", O_RDONLY) = -1 ENOENT (No such file or directory)
access("/usr/share/dracut/modules.d/01fips", F_OK) = -1 ENOENT (No such file or directory)
open("/dev/null", O_RDWR) = -1 EACCES (Permission denied)
write(2, "Couldn't open /dev/null: Permiss"..., 43Couldn't open /dev/null: Permission denied
) = 43
exit_group(1) = ?
the full strace is viewable here :
http://pastebin.com/5SS6K0Nu