Checking Web Server Version Using Command Line

We usually use these methods to verify what is being displayed in our HTTP header to the public. There are 2 tools that can be used, curl and wget.

To use wget:

$ wget --server-response --spider http://www.mydomain.com

...

Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips mod_fcgid/2.3.9

...

To use curl:

$ curl --head http://www.mydomain.com

...

Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips mod_fcgid/2.3.9

...

Accessing MTP Mounted Device Via Command Line

When you connect your android phone to a linux box using usb cable, the storage of the phone will appear in your file manager (thanks to automount). It is easily accesible from there, but what if you want to access it via command line? Where is it located?

To know the location of the MTP mounted storage, you need to know your user id

$ id

uid=1000(user) gid=1000(user) groups=1000(user),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),114(lpadmin),134(sambashare)

From the above command, the user ID is 1000. The MTP mounted device can be accessed at /run/user/<user ID>/gvfs

$ ls /run/user/1000/gvfs/

'mtp:host=Android_Android_28f5d3440504'

Just go to the 'mtp:host=Android_Android_28f5d3440504' directory (the name might differ), and you will see your phone's storage.

 

 

 

 

Getting Access Denied Error when Using systemctl as root

 I got this error in one of our server, when trying to restart nginx

# systemctl status nginx

Failed to get properties: Access denied

Does not make sense, I am a root user. After some searching, a few suggestions came. 

The first suggestion was to restart systemctl daemon:

# systemctl daemon-reexec

That did not work for me. Another solution is to disable selinux temporarily, but this also did not work for me:

# setenforce 0 

The last thing that I tried (that actually worked) was to sending sigterm to systemd, and it will restart by itself:

# kill -TERM 1

If you guys happened to encounter this sort of error, you can try all the above. Some might suit you better than the other.

Installing elinks in CentOS 8

Elinks is a text based web browser, and it is now available in powertools repository. Powertools repository is not enabled by default, thus elinks is not available to be installed just by using standard yum install command.

List all available repositories

$ sudo yum repolist --all

...

powertools

...

Install elinks while enabling powertools repository temporarily

$ sudo yum install --enablerepo=powertools elinks -y

...

Installed:

  elinks-0.12-0.58.pre6.el8.x86_64                                                     gpm-libs-1.20.7-15.el8.x86_64                                                    

Complete!

Congratulations, you can now use elinks to view any website, but only in text based mode.

Fixing Wrong Timezone in Docker Logs

I had this issue of my running container logs is using UTC as its timezone, which will make troubleshooting process quite troublesome.

After some experiment, I found that we have to set the timezone early when we run the container, to make the logs recorded in the timezone we prefer.

For currently running container, the safest way is to commit it to image, and rerun a new container based on that image.

1. My current container's logs

$ docker logs mycontainer

...

2021-03-09 12:01:08.939 UTC [1283819] WARNING:  terminating connection because of crash of another server process

...

2. Back up the current container to an image called mycontainer-backup:20210310

$ docker commit mycontainer mycontainer-backup:20210310

3. Stop the current container, to avoid port clash (if any)

$ docker stop mycontainer

4. Run a new container, based of the backup image, this time we need to specify the timezone variable

$ docker run -dit --name mynewcontainer -e TZ=Asia/Kuala_Lumpur mycontainer-backup:20210310

5. Done, we can verify the log's timezone, just to be sure

$ docker logs mynewcontainer

...

2021-03-10 08:03:14.429 +08 [1] LOG:  listening on IPv4 address "0.0.0.0",

...