Each file can has a set on permissions: read(r), execute(x) and write(w).
These permissions can be applied to user, group and all. So you will have a read permission for the user, a write permission for the user and so on.
In a listing (for example when you do "ls -la /") this is encoded in the following way: for each permission just one letter is used if it is available (like rwx if all are available) and a - if it is not available (like ---).
As we have 3 permissions for user, group and all we end up with 9 charachters like: "rwxr-x---" (which means user has all permissions, group doesn't have write and all doesn't have any).
You should check that the directory in which you want to write your backup can be written by user db2inst1. This means one of the following must be true:
- the directory is owned by db2inst1 and the user has write permissions
- the directory's group is one in which the user db2inst1 is found, and the directory has write permissions for the group.
- the directory can be written by anybody.
I wouldn't recommend letting the process doing the backup in /root. If it has a specific home, you can do the backup there and copy it afterwards.
If you really want to do that, you could add db2inst1 to the group that owns /root directory (gpasswd -g db2inst1 group_of_root_dir) and give write permissions to the group (chmod g+w /root). For more info you can check "man gpasswd" and "man chmod".