：Troubleshoot duplicate or invalid df mount paths on CentOS 6

Problem description

On a CentOS 6 ECS instance, df -h returns duplicate or non-existent mount paths.

Cause

/etc/mtab is not symbolically linked to /proc/self/mounts, causing df to return abnormal output.

Normally, /etc/mtab is a symbolic link to /proc/self/mounts. When this issue occurs, /etc/mtab is a regular file. Run ll /etc/mtab to verify.

Solution

1. Check /proc/self/mounts and confirm that mount information for all file system partitions is correct.

   cat /proc/self/mounts

2. Back up /etc/mtab and replace it with a symbolic link to /proc/self/mounts.

   # Back up the mtab file
   mv /etc/mtab /etc/mtab.bak
   # Create a symbolic link to /proc/self/mounts
   ln -s /proc/self/mounts /etc/mtab

3. Run df -h again to verify the output. If invalid mount paths persist, unmount them with the umount command.