The most common and most likely answer to this crossword clue is the 3 plus 3 letter word LOG OFF
I've seen this crossword clue in The Guardian
L
O
G
O
F
F
More clues leading to the result LOG OFF
- Look, try force twice to end session
- Stop using computer symbol with great noise
- Leave computer brand staffing centre
- Leave session of golf confused
- ymbol’s very powerful, shut down
- Coach of golf to quit working online
- End session on computer when record of voyage concludes ‘zero fathoms’
- Brand’s very loud exit
- Shut down record of First Folio
- Exit computer session of golf play
Buddy explains!

The straight part
We know that "shut down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shut down = log off.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.