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Replace 'username' with your username on Narval. The 'narval' above is just a name given to this "host". You can put here any name you like that does not already exist in your ~/.ssh/config. The '10m' means that you will be able to log in without authentication up to 10 minutes after you closed your last connection to Narval from the same machine. Possible time units for ControlPersist are:
none: seconds, s | S : seconds, m | M: minutes, h | H: hours, d | D: days, w | W: weeks
Combinations are also possible, for example: 1h30m → 1 hour 30 minutes (90 minutes)
Windows users
Check out the wiki of The Alliance: Multifactor authentication
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