This is a standard procedure for me, whenever I set up a new Raspberry Pi system. Because the default user is "pi", I quickly replace it with my own (e.g. "kostis"), but I have to substitute that user to all of pi's groups first, before deleting the default account. xargs helps a lot with that in a single line, while avoiding boring "for" loops. For everything trickier, there's always "parallel" :)

Alternatively, the kernel provides a script to cleanly compare two config files even if the options have moved in the file itself: /usr/src/linux/scripts/diffconfig .config.old .config

Because Mac app bundles contain everything in one place, it makes running them from anywhere, including from a device such as a USB flash drive or external HDD, possible. So if your Mac has a mere 256GB of storage (as mine does), you can free up large quantities of disk space by storing apps like, say, Xcode on external devices.

It is the same but more faster real 0m0,007s user 0m0,011s sys 0m0,000s with my solution real 0m0,038s user 0m0,044s sys 0m0,000s with your solution :) Show Sample Output

Thanks to this user: https://stackoverflow.com/a/35636373/2394635 Show Sample Output

Adding this alias to ~/.bashrc or, better yet, the system-wide /etc/bash.bashrc (as in my setup) will make it possible to not only run pacman as any user without needing to prepend sudo but will also ensure that it always assumes that the user knows what he or she is doing. Not the best thing for large multi-user enterprise setups at all to say the least, but for home (desktop) use, this is a fantastic time-saver.

This is useful if you add sid, install some packages, then remove sid and want to work out which packages you installed from sid that should be removed (e.g. before an upgrade to the new stable). Alternatively you can think of this as "find installed packages that can no longer be installed."

Use lsbk (list block) and jq (to manipulate a JSON on the command line) to display partition information: Show Sample Output

It repeats a command, such as free, every five seconds and highlights the differences

Sometimes things break. You can find the most recent errors using a combination of journalctl, along with the classic tools sort and uniq Show Sample Output

Raise your hand if you haven't used this at least once to share a directory quickly

The shell {} operator is great for this. Here's an example with three directories enclosed in {}:

https://wuseman.nr1.nu:8080/file/E8AcLVgMPZ2LSJQf/9BD8V8ADYNhR6cca/parallel_print_progress.gif Show Sample Output

Breakdown of the subshell: cat /etc/group # contents of file containing all groups on the system grep -v 65534 # filter out the ‘nobody’ group cut -d\: -f1 # extract the group names themselves tr ‘\n’ ‘,’ # replace all new lines in the extracted output with commas sed -e “s/\,$//“ # remove trailing comma from the end of the output After rebooting, if you type the “groups” command, you’ll find yourself added to (almost) every group on the system.

Should run anywhere that Bash works.. Your mileage may vary. Show Sample Output

After downloading an ISO image, assuming you have QEMU installed, it’s possible to boot an ISO image in a virtual machine and then install that ISO from within the virtual machine directly to a physical drive, bypassing the need to reboot. Simply pass the ISO image as the -cdrom parameter, followed by “format=raw,file=/dev/sdb” (replace /dev/sdb with the drive you want to install to) as the hard drive parameter (making absolutely certain to specify the raw format, of course). Once you boot into the ISO image with QEMU, just run the installer as if it were a virtual machine — it’ll just use the physical device as an install target. After that, you’ll be able to seamlessly boot multiple distros (or even other operating systems) at once.

Lists all installed kernels minus the current one. This is useful to uninstall older kernels that take too much space on /boot partition. Show Sample Output

This is a very hackish way to do it that I'm mainly just posting for fun, and I guess technically can more accurately be said to result in undefined behavior. What the command does is tell the shell to treat libpng like it's a shell plugin (which it's most certainly not) and attempt to install a "png_create_read" command from the library. It looks for the struct with the information about the command; since it's always the command name followed by "_struct", it'll look for a symbol called "png_create_read_struct". And it finds it, since this is the name of one of libpng's functions. But bash has no way to tell it's a function instead of a struct, so it goes ahead and parses the function's code as if it was command metadata. Inevitably, bash will attempt to dereference an invalid pointer or whatever, resulting in a segfault.

Useful when you wait for a server to boot up.