Information
Users can be defined in /etc/passwd without a home directory or with a home directory that does not actually exist.
If the user's home directory does not exist or is unassigned, the user will be placed in "/" and will not be able to write any files or have local environment variables set.
Solution
If any users' home directories do not exist, create them and make sure the respective user owns the directory. Users without an assigned home directory should be removed or assigned a home directory as appropriate.
The following script will create a home directory for users with an interactive shell whose home directory doesn't exist:
#!/bin/bash
awk -F: '($1!~/(halt|sync|shutdown|nfsnobody)/ && $7!~/^(/usr)?/sbin/nologin(/)?$/ && $7!~/(/usr)?/bin/false(/)?$/) { print $1 " " $6 }' /etc/passwd | while read -r user dir; do
if [ ! -d "$dir" ]; then
mkdir "$dir"
chmod g-w,o-wrx "$dir"
chown "$user" "$dir"
fi
done