I am trying to install ceph in ubuntu 16.04 by this link
It's kind of hard to support someone elses documentation, you should really have started with contacting them about their process if it doesn't work.
but when I am run this command #ceph-deploy install ceph-deploy monnode1 osd0 osd1
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$ sudo apt-get install ceph-common
ceph-common is already the newest version (12.2.12-1xenial).
ceph-common set to manually installed.
...
Setting system user ceph properties..usermod: user ceph is currently used by process 1648
Seems like this machine is half-installed already, which probably is why the automated scripts are failing, they aren't considering the case when you already have a ceph user running a process while trying to add a ceph user. You should start over from a clean machine and not from a box where half of the packages are already running programs.
May the most significant bit of your life be positive.