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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?

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“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

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