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LVM2 Reduce
Just the commands for the lvreduce I keep forgetting.

Add forgotten changes to the last git commit
It's pretty common to forgot to commit a files, be it a modification, or a brand new file. If you did forget something, git add the files you want, and then git commit --amend. It will essentially redo the last commit, with the changes you just added. It seeds the commit message with the last commit message by default. You probably shouldn't do this if you've already pushed the commit.

Determine space taken by files of certain type
Just how much space are those zillions of database logs taking up ? How much will you gain on a compression rate of say 80% ? This little line gives you a good start for your calculations.

Remove a line in a text file. Useful to fix "ssh host key change" warnings

Count lines in a file with grep
Returns the number of lines in a file, emulates "wc -l" behavior with grep.

Rename files to be all in CAPITALS
Simple bash/ksh/sh command to rename all files from lower to upper case. If you want to do other stuff you can change the tr command to a sed or awk... and/or change mv to cp....

Set laptop display brightness
Run as root. Path may vary depending on laptop model and video card (this was tested on an Acer laptop with ATI HD3200 video). $ cat /proc/acpi/video/VGA/LCD/brightness to discover the possible values for your display.

Add page numbers to a PDF
Put this code in a bash script. The script expects the PDF file as its only parameter. It will add a header to the PDF containing the page numbers and output it to a file with the suffix "-header.pdf" Requires enscript, ps2pdf and pdftk.

Quickly (soft-)reboot skipping hardware checks
If you are doing some tests which require reboots (e. g. startup skripts, kernel module parameters, ...), this is very time intensive, if you have got a hardware with a long pre-boot phase due to hardware checks. At this time, kexec can help, which only restarts the kernel with all related stuff. First the kernel to be started is loaded, then kexec -e jumps up to start it. Is as hard as a reboot -f, but several times faster (e. g. 1 Minute instead of 12 on some servers here).

Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }


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