System Administration on Sandro Cirulli

How to zip and unzip from the command line

Fri, 29 May 2015 00:00:00 +0000

Image: Roadsidepictures – CC BY-NC-ND 2.0

There are lots of GUI utilities to zip and unzip files but sometimes you only have access to the command line on a machine. Linux has different types of data compression formats (.tar, tar.gz, tar.bz2, etc.) but I find the zip utilities easier to use and more compatible with Windows systems. So how do you zip and unzip files from the command line?

How to install Groovy on Linux system-wide

Sun, 24 May 2015 00:00:00 +0000

Image: Groovy Logo, The Apache Software Foundation, Apache License 2.0

A colleague of mine recently asked me to install the Groovy programming language on our Red Hat 6.5 server and to make it accessible to all users. I thought it would be a very straightforward task but a quick search on the Red Hat 6.5 official repositories didn’t return any package for Groovy.

The easiest way to install Groovy manually is via sdkman. I followed this procedure to do it:

How to change timezone on a Linux server

Sun, 17 May 2015 00:00:00 +0000

Image: deckhand – CC BY-NC-ND 2.0

Every year in March and in October the clock changes in most countries for energy saving purposes. This has the annoying effect of messing up the current time on your server if the timezone is not set properly. Servers in Europe are often set up to UTC time. For example my web hosting provider explicitly says:

Note that any times specified are executed in the timezone of the server, and not your local timezone. Accordingly, you may need to make allowance for this when selecting when to run your cron job. Our servers run in the ‘UTC’ timezone because our client base is global, and it remains constant throughout the year with no changes for daylight saving.

How to add a new user with sudo rights

Sat, 16 May 2015 00:00:00 +0000

Image: xkcd – CC BY-NC 2.5

Let’s say you have a new user needing sudo access to a Linux server. How do you grant him/her this great privilege? First, explain to the new user that sudo rights allow to do pretty much anything on a Linux machine – including screwing everything up! – and that with greater power also comes greater responsibilities. Then, follow this procedure:

Create a new user (e.g. newusername) and add it to group wheel (members of this group have sudo rights):
```
sudo useradd -G wheel newusername
```
Set up the password for the new user. First, login as root:
```
sudo -i
```
Then set the password for the new user (e.g. newusername):
```
passwd newusername
```
Finally exit from root with:
```
exit
```
Test the newly created user and password by logging in as user newusername:
```
su - newusername
```
Test that the newly created user is in group wheel:
```
groups newusername
```