mount -t cifs //ip/c$ /mnt/System/ -o username=administrator,password=<pw>
umount /mnt/System/

mount -t cifs //ip/c$ /mnt/System/ -o credentials=/root/ies.info/server.login -v
mount error(13): Permission denied
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
ll /root/ies.info/server.login
-rw------- 1 root   root     server.login
cat /root/ies.info/server.login
username=administrator
password=<pw>