How to grap old all messages after rebooting the QFX VC?
Logs roll over to save space so don't persist long but there are generally 5 files of each log type. The main general log file is messages.
you can see all available files with:
show log ?
the current file is just the name.
previous versions have ,#.gz and can also be viewed
show log messages
show log messages.0.gz
you can use match to find specific lines
show log messages | match error
or just the last few lines
show log messages | last 100