Today, on my Centos server I tried to add a user but got the following error:

-bash: /usr/sbin/useradd: Input/output error

How do I fix it?


“Input/output error” indicates something that shouldn't happen somewhere in the input/output stack. The intended meaning is a hardware failure: your hard disk is failing.

Often this error turns up in cases where the problem is a software bug or a misuse of a special-purpose filesystem. But here, you're reading from a system directory, so a hardware failure is the most likely explanation.

RAM also tends to fail, so when you see an inexplicable error, do test your RAM.

  • OK I see...What I maybe forgot to mention is that the Server is a VPS... So I guess a restart might fix it? – DextrousDave Aug 12 '13 at 4:03
  • @DextrousDave A restart might make the symptom go away, but it can't fix the problem. On a VPS, there's also a chance of a bug in the virtualization layer. Investigate a little more (for example, is this fully deterministic?) and contact your hosting provider's support. – Gilles Aug 12 '13 at 7:35
  • I contacted my Service Provider and they restarted the server from their end. The problem is now resolved, they also cannot give me a definitive answer, so I will have to monitor the OS closely. Thanks for the help – DextrousDave Aug 16 '13 at 9:43
  • how to test RAM? – user4951 Oct 5 '13 at 2:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.