create /dev/null file (in case it was accidentally removed)
mknod /dev/null c 1 3 chmod 666 /dev/null
numbers can be checked on other working maching like
liutyi@server2:~$ ls -la /dev/ |grep "root 1" crw-rw-rw- 1 root root 1, 7 Jan 27 00:57 full crw-r--r-- 1 root root 1, 11 Jan 27 00:57 kmsg crw-rw-rw- 1 root root 1, 3 Jan 27 00:57 null crw-rw-rw- 1 root root 1, 8 Jan 27 00:57 random crw-rw-rw- 1 root root 1, 9 Jan 27 00:57 urandom crw-rw-rw- 1 root root 1, 5 Jan 27 00:57 zero
same way is to create /dev/zero /dev/random and other special device files
