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Show GCC-generated optimization commands when using the "-march=native" or "-mtune=native" switches for compilation.
You can tell GCC to automatically select optimization commands and produce optimized code for the local machine (the one compiling the code), but you can't normally see what switches have been selected and used unless you append a "-v" and pause compilation.

force a rescan on a host of scsi devices (useful for adding partitions to vmware on the fly)

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" }

Check which files are opened by Firefox then sort by largest size.
Just refining last proposal for this check, showing awk power to make more complex math (instead /1024/1024, 2^20). We don't need declare variable before run lsof, because $(command) returns his output. Also, awk can perform filtering by regexp instead to call grep. I changed the 0.0000xxxx messy output, with a more readable form purging all fractional numbers and files less than 1 MB.

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

find sparse files
Prints the path/filename and sparseness of any sparse files (files that use less actual space than their total size because the filesystem treats large blocks of 00 bytes efficiently).

To have only unique lines in a file

Regenerate the /etc/mtab file

convert wmv into xvid avi format

Use bash history with process substitution
Bash has a great history system of its commands accessed by the ! built-in history expansion operator (documented elsewhere on this site or on the web). You can combine the ! operator inside the process redirection


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