Solaris

I compared inittab with another working system and they are identical...

This is how it looks like:

# cat /etc/passwd
root:x:0:1:Super-User:/:/bin/ksh
daemon:x:1:1::/:
bin:x:2:2::/usr/bin:
sys:x:3:3::/:

Do you think it is worth changing ksh to sh?

ALWAYS keep root's shell as /sbin/sh. Call ksh or whatever shell you want to use after su'ing to root.

Show us what you've got in /etc/vfstab, I think sbk1972 makes a great point.

This is what it shows:

# cat /etc/vfstab
#device device mount FS fsck mount mount
#to mount to fsck point type pass at boot options
#
#/dev/dsk/c1d0s2 /dev/rdsk/c1d0s2 /usr ufs 1 yes logging
#/dev/dsk/c2t0d0s0 /dev/rdsk/c2t0d0s0 /oracle ufs 1 yes logging
#/dev/dsk/c2t0d0s0 /dev/rdsk/c2t0d0s0 /shared_disk/oracrs ufs 1 yes logging
#/dev/dsk/c2t0d0s1 /dev/rdsk/c2t0d0s1 /shared_disk/oradata ufs 1 yes logging
#/dev/dsk/c2t0d0s2 /dev/rdsk/c2t0d0s2 /shared_disk/flash_recovery_area ufs 1 yes logging
fd - /dev/fd fd - no -
/proc - /proc proc - no -
#/dev/md/dsk/d0 /dev/md/rdsk/d0 / ufs 1 no logging
#/dev/dsk/c1t0d0s1 - - swap - no -
#/dev/dsk/c1t0d0s7 /dev/rdsk/c1t0d0s7 /export/home ufs 1 yes logging
/dev/md/dsk/d1 - - swap - no -
/dev/md/dsk/d0 /dev/md/rdsk/d0 / ufs 1 no logging
/dev/md/dsk/d2 /dev/md/rdsk/d2 /export/home ufs 2 yes logging
swap - /tmp tmpfs - yes -

I will change to /sbin/ksh and give it a try...

No!! Don't use /sbin/ksh!
Use /sbin/sh


your vfstab looks OK but it makes me suspicious. Please post the output of `df` while in multi-user mode.