Software RAID has come a long way. Unless you have some very high-rate, high-volume, I/O workloads with SLAs that will otherwise cost you money, for the most part a software RAID will perform just fine. One of the primary benefits of using software RAID is the portability of your disks/data. If a box on which you have a software RAID dies somehow and at least some (depending on your RAID configuration) of drives survive, you can easily resurrect the RAID → Continue reading “Setting up software RAID on Debian with mdadm”
Category: Linux
[SOLVED] debsig-verify for Failed verification error, “signatures using the SHA1 algorithm are rejected” and “Can’t check signature: Invalid digest algorithm”
If you are using debsig-verify for the verification of a downloaded .deb file and are unable to verify it, run it with the -d option to get more information. If you see the following two lines
gpg: Note: signatures using the SHA1 algorithm are rejected
gpg: Can't check signature: Invalid digest algorithmIt is likely that the PGP signature used to sign the package uses the SHA1 algorithm which has been deprecated in most of the recent Linux distros. If → Continue reading “[SOLVED] debsig-verify for Failed verification error, “signatures using the SHA1 algorithm are rejected” and “Can’t check signature: Invalid digest algorithm””
LVM Resize – reduce the size of one logical volume to enable expanding another
I’m running an Ubuntu workstation and when setting it up simply went the “next-next-next” route when setting up the encrypted disk via LVM. The default is to create a 1G swap partition which is just not enough when you attempt to run too many things and locks up and/or crashes the machine.
My goal was to reduce my /root partition and then use that space to extend my swap partition.
Ensure that you back up your data first! There is → Continue reading “LVM Resize – reduce the size of one logical volume to enable expanding another”
Use printf to join an array in Bash
If you would like to join an array of elements with a defined delimiter in Bash there is an easy way to go about it by using printf. Following is an example
#!/bin/bash
declare -a arr=()
for i in `seq 1 5`
do
arr=("${arr[@]}" $i)
done
# Generate a single string joined by a comma. The printf string can contain
# any arbitrary delimiter.
printf -v joined '%s,' "${arr[@]}"
# Print out the string minus the trailing comma
echo Diffing the output of two commands
The GNU diff command on most Linux and UNIX systems will diff the contents of two files. With Bash, you can, using process substitution, take the output of any arbitrary command and process its input, or output, as a file descriptor. In this way, you can then use diff against the output of two commands as follows
diff <(cmd1) <(cmd2)Both cmd1 and cmd2 will appear as a file name/file descriptor. The < character indicates that the file descriptor should → Continue reading “Diffing the output of two commands”
How to check if a file is sourced in Bash
Sometimes you will want to ensure that a file is sourced instead of executed. This ensures, among other things, that any environment variables that the script defines remain in your current shell after the script completes.
To do so, use the following to check whether the file was sourced or run in a sub-shell
(return 0 2/dev/null) && sourced=1 || sourced=0
echo "sourced=$sourced"Bash allows return statements only from functions and in a scripts top level scope IF it → Continue reading “How to check if a file is sourced in Bash”
Pruning directories from find
I have no idea why, but for some reason I always have a hard time remembering the exact syntax for find when I want to prune some list of directories from a search.
Let’s say that you want to execute a find in a directory where there are a lot of .git directories and you don’t want to search through the guts of the repo directories. With the following command we specify the prune predicate ahead of the search for → Continue reading “Pruning directories from find”
Using cut with a delimiter of any amount of whitespace
The TLDR; is to first use tr to replace all occurrences of any horizontal whitespace character with a single space, and then squeeze down any number of spaces to a single space and then define the delimiter for cut as a single space. The following example assumes that you want to see from the 5th column to the end of the line.
<do-something-to-generate-input| tr '[:blank:]' ' ' | tr -s ' ' | cut -d ' ' -f5-The → Continue reading “Using cut with a delimiter of any amount of whitespace”
Running GUI apps locally as root in a non-root session
There are instances when you need to run an X Window application. For me this is often running a terminator instance as root so that I can create tabs and split the window as still be root in each of those terminals.
In order for the root user to be able to connect to the X server you need to provide it with “credentials”. In this case it is on the same box and not over the network so the → Continue reading “Running GUI apps locally as root in a non-root session”
Using fc to Edit and Re-execute Bash Commands
I recently learned about the Bash built-in fc. It is a great tool that enables you to edit and re-execute commands from your bash history.
Oftentimes there is a command in your history that instead of just grepping through the history and then re-executing as-is you’ll want to make a modification or two. With fc you can first edit it in your favorite editor and then when closing the editor fc will execute the command.
For me, vim is my → Continue reading “Using fc to Edit and Re-execute Bash Commands”