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Using Or on Regular Expressions

Here’s a regex using the pipe symbol as OR to allow only 6 possible values. 

regex="efs-(00|04|08|12|16|20)00"

Matches:

efs-0000
efs-0400
efs-0800
efs-1200
efs-1600
efs-2000

No matches:

efs-0100
efs-2200
efs-0600
efs-1400
efs-1800
efs-1110
111022
asdb023
2330asd
1200-efs
1205
abc

$var is compared with $regex to find a match. $var is any of the variables above.

if [[ $var != $regex ]]; then
  echo "Not a match"
else
  echo "It's a match"
fi

Setup Log Rotation

Logrotation is available in most Linux distros. If they are missing, you can easily install them. The logrotation main configuration file is located in /etc/logrotate.conf which is the default setting. The config file contains an include statement that pulls in other log configurations located in the /etc/logrotate.d/ directory. When setting up a log rotation, it’s best to add your log rotation configuration in this directory.

Here’s a simple configuration in a file called webmon.

/home/ubuntu/webmon.log {
        daily
        create 0640 ubuntu ubuntu
        dateext
        rotate 7
	nocompress
}

The options above does the following:

  • The logs are rotated daily.
  • The logs are rotated 7 times with no compression.
  • The rotate log files will have dates appended to them.
  • The log files are owned user ubuntu with permission of 0640.

There are more options from the logrotate man pages which can be added.

Mounting Duplicate UUIDs

While trying to recover a directory from backup, I ran into an issue with duplicate uuids when trying to mount a recovered volume. The problem was the recovered volume had the same uuid as boot.

Here’s the original mount command I ran, but I was getting a wrong fs type error.

mkdir
mount -t xfs /dev/nvme3n1p2 /recover
mount: wrong fs type, bad option, bad superblock on /dev/nvme3n1p2,
       missing codepage or helper program, or other error

It turned out to be a duplicated uuid. To get around this problem, I ran -o nouuid.

mount -t xfs -o nouuid /dev/nvme3n1p2 /recover

Once the files were recovered, I unmounted volume and detached it from the instance.