Fault description

[root@client1 home]# ls /
ls: cannot access /com: Host is down

Cause of the failure
There is a folder in your current directory that is a network folder, and this folder points to a folder on a remote host on the network.
And when you use ls now, the remote host has been shut down, this will happen.

Solution
umount /com
comment /etc/fstab about the content of /com