Why yum fails on system with "No module named yum" error ?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux (RHEL)

Issue

  • Performing yum update results in the error "No module named yum"
  • While running "sosreport" fails with "No module named os"

Resolution

  • Unset the PYTHONHOME variable:
    # unset PYTHONHOME

For permanent change remove entry from root's .bashrc or .bash_profile if present.

  • Reinstall python package by running following command:
      # rpm -Uvh --replacefiles --replacepkgs python-<version>.rpm

Root Cause

  • PYTHONHOME variable was set as environment variable on system.
  • Python libraries/files are modified which can be observed from output of rpm -Va command.
  • Third party python modules are installed on system which found in output of "ldd /usr/bin/python" command.
  • The package rpm-python* is not installed.

Diagnostic Steps

# sosreport 

'import site' failed; use -v for traceback 
Traceback (most recent call last): 
  File "/usr/sbin/sosreport", line 29, in ? 
    import os 
ImportError: No module named os 

# yum -d10 update
'import site' failed; use -v for traceback 
There was a problem importing one of the Python modules 
required to run yum. The error leading to this problem was: 

   No module named yum 

Please install a package which provides this module, or 
verify that the module is installed correctly. 

It's possible that the above module doesn't match the 
current version of Python, which is: 
2.4.3 (#1, Jul 16 2009, 06:20:46) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-44)] 

If you cannot solve this problem yourself, please go to 
the yum faq at: 
  http://wiki.linux.duke.edu/YumFaq  

Collect the following details from system

# rpm -qa --queryformat "%{NAME}-%{VERSION}-%{RELEASE}-%{ARCH}\n" | sort > /tmp/rpm-list
# ldd /usr/bin/python

Strace command output
# strace -fxvto /tmp/strace.out yum update 

# which python
# env > /tmp/env.out 
# rpm -qf `which yum`
# rpm -Va > /tmp/rpm_va

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