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run sync first to flush useful things out to disk!!!
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
Do not run this command if you already have ntpd running!
This needs to run as root, for example with sudo:
sudo ntpdate pool.ntp.org && sudo hwclock --systohc && sudo hwclock --adjust
This command will fetch accurate time from NTP servers and synchronize your system clock, then it will use the system clock to synchronize your hardware clock, and will calculate the time drift.
Find all corrupted jpeg in the current directory, find a file with the same name in a source directory hierarchy and copy it over the corrupted jpeg file.
Convenient to run on a large bunch of jpeg files copied from an unsure medium.
Needs the jpeginfo tool, found in the jpeginfo package (on debian at least).