Linux – Login the Linux with root ,executing command sshd、tcpdump failed

    root# /usr/sbin/sshd
    Privilege separation user sshd does not exist

    root# tcpdump -i eth0 udp  
    tcpdump : Couldn't find user 'tcpdump'

but the users tcpdump and sshd are in the files /etc/shadow and /etc/passwd

   root # cat /etc/passwd
   root:0:0:root:/root:/bin/bash
   bin:1:1:bin:/bin:/sbin/nologin
   daemon:2:2:daemon:/sbin:/sbin/nologin
   ftp:14:50:FTP User:/var/ftp:/sbin/nologin
   oprofile:16:16:Special user account to be used by OProfile:/home/oprofile:/sbin/nologin
   tcpdump:72:72::/:/sbin/nologin
   sshd:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
   named:25:25:Named:/var/named:/sbin/nologin
   qmaild:505:504::/var/qmail:/bin/false
   qmaill:506:504::/var/qmail:/bin/false
   qmailp:x:507:504::/var/qmail:/bin/false
   qmailq:x:508:505::/var/qmail:/bin/false
   qmailr:x:509:505::/var/qmail:/bin/false
   qmails:x:510:505::/var/qmail:/bin/false
   apache:x:48:48:Apache:/var/www:/sbin/nologin
   mysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/bash
   dump:x:0:0::/tmp:/bin/dumpsh

   root # cat /etc/shadow
   root1$eigU8oI6$jYOcUeV1dunekVie/GWeL0:15264:0:99999:7:::
   dump1$mJQ/PAm7$t0JvrCVFDW2I/m2quQSd90:15391:0:99999:7:::
   bin:*:14789:0:99999:7:::
   daemon:*:14789:0:99999:7:::
   ftp:*:14789:0:99999:7:::
   oprofile:!!:14946::::::
   tcpdump:!!:14946::::::
   sshd:!!:14946::::::
   named:!!:122391:0:99999:7:::
   apache:!!:15191::::::
   mysql:!!:15191::::::

If there were someone know how to solve this problem,please help me.
Thank you very much.