I am on CentOS I know this is Ubuntu but bear with me, this still comes top on google. People are correct to say that mount -a
will give you the error.. on centos you then have to type # dmesg
which will tell you what was actually wrong in detail
For me, I had to change
# cat /etc/centos-release
CentOS release 6.9 (Final)
# nano /etc/fstab
------------------------------------------------
\\192.168.0.4\Work /mount/drive cifs user,rw,suid,uid=48,umask=0777,username=*****,password=******* 0 0
to
# cat /etc/centos-release
# CentOS Linux release 8.2.2004 (Core)
# nano /etc/fstab
------------------------------------------------
\\192.168.0.4\Work /mount/drive cifs user,rw,suid,uid=48,file_mode=0770,dir_mode=0770,username=*****,password=******* 0 0
the error I got was under dmesg
was CIFS: Unknown mount option "umask=0777"
note that umask is no longer allowed
man
page?dmesg | tail
tells you a bit more about which option is giving you trouble.