The Stupid Minds

The dd utility can be successfully used to create a backup of a filesystem (in lack of more specialised backup utilites).

dd if=/dev/sdaX | gzip > /backup/sdaX.gz

where sdaX is the partition you want to backup, and the /backup folder is located on a different disk/partition than the one you’re backing up..

Only note that dd does not care whether a sector is used or not, it will copy it to the image file nonetheless. Zeroing out all free space before backup up is a good way to keep wasted backup space to a minimum (since the backup will be compressed)

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This function comes in handy when you want to make a compressed sector-by-sector backup of the filesystem and you don’t want to include/waste space with the unused sector (which still have information on them)

Running

nice cat /dev/zero > zero.fill;sync;sleep 1;sync;rm -f zero.fill

before the actual backup will make sure all unused sectors contain zero (so they will not waste any space in the archives).

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If you ever need to count the occurences of a character in all (or some) files, this next series of commands would come in handy:

for f in `ls`; do cat $f; done | awk ‘{ for ( i=1; i<=length; i++ ) arr[substr($0, i, 1)]++ }END{ for ( i in arr ) { print i, arr[i] } }’ | grep X

Replace X with the character in question. The command is all in one line. “ls” can be replaced with a more specific list (eg: “ls *.c“)

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