Data Domain reached 100% of capacity utilization

Key questions here are how are you using DD and do you know why it happened?  I assume you do monitor space and if it happened out of the blue it should be easy to see what contributed to this.  Once you know this, removing what caused this should be done via app which is using it (this is why we ask how you are using it).  As this is DDVE as per tag you mentioned, I assume you could just add more disk?

Actually i know from early it reached above 95 % and we must upgrade it or tech refresh, but now we are in process of buying new one, so i need to free some space from the box till new box delivery. so i ask does there any command that indicates data retention to the box and how to clear the oldest data.

Normally it will be backup application (or application if using directly writes to DD w/o bck app) which takes care of retention.

Cleanup on DD runs once per week.  For example, you can see how much can be removed now via df command:

# df

Active Tier:

Resource          Size GiB    Used GiB  Avail GiB  Use%  Cleanable GiB*

----------------  --------  ---------  ---------  ----  --------------

/data: pre-comp          -  1267533.2          -      -                -

/data: post-comp  301029.8    224697.2    76332.6    75%          24456.4

/ddvar                29.5        9.3        18.8    33%                -

----------------  --------  ---------  ---------  ----  --------------

* Estimated based on last cleaning of 2017/02/07 12:09:58.

In above example, DD can remove 24TiB. This will be done on next run or you can kick it in by running filesys clean start command.  However, since you have small amount of space, it will be slow and if it is 100% full I doubt it can run.

AbdelazizHammad  does this document help answer your question Data Domain: How to resolve issues with high space utilisation or a lack of available capacity on Data Domain Restorers (DDRs) is yes can you mark the question as resolved if one of the other answers fits please mark it as resolving

clean can run at 100% usage, i can confirm that, its one of the standard first steps. get as much free space back as possible so that the backup application (ie avamar) can do its maintenance tasks and mark more disk as cleanable

it can be worth adding an additional clean cycle a week, but seriously try and avoid doing it daily, EMC give you evil looks if you do it more than twice a week... as the more often it runs the more chance of something unfortunate happening. of course nothing bad might happen, but don't bank on it.