Troubleshooting

1.0 Error

While configuring a Linux server, the error Failed to fetch webpage, temporary failure resolving domain was observed.

$ sudo apt-get update
Err:1 ... bionic InRelease
  Temporary failure resolving ...
Err:2 ... bionic-updates InRelease
  Temporary failure resolving ...
...
Reading package lists... Done
W: Failed to fetch ...  Temporary failure resolving ...
...

Also, the

1.0 Error

After updating the Drupal 7 version in a website, the following error was observed in the configuration of the Composer Manager module.

Composer Manager: Composer's install command must be run to generate the autoloader and install the required packages.

The above message was followed by the status of packages managed by the Composer. ...

1.0 Error

After updating the website to a new version of Drupal 7, the following error was printed on the web pages.

Notice: Trying to get property of non-object in block_block_view() (line 247 of modules/block/block.module).

2.0 Resolution

The error was resolved by the following steps.

2.1 Turn off block caching

From the Administration menu, Select Configuration –> Development ...

1.0 Error:

While configuring the Dovecot Mail Delivery Agent, the Dovecot server would not start and the following error messages were printed.

$ sudo systemctl start dovecot
Job for dovecot.service failed because the control process exited with error code. See "systemctl status dovecot.service" and "journalctl -xe" for details.
$ systemctl status dovecot.service
● dovecot.service - Dovecot IMAP/POP3 ...

1.0 Error

PHP code was not getting executed in the index.html file when the concerned website was opened in a browser. nginx server was being used to serve the web pages.

2.0 Solution

2.1 Install php7.0-fpm

$ sudo apt-get install php7.0-fpm

2.2

1.0 ERROR

A website stopped opening in browser, giving the error that the SSL certificate was either invalid or had expired.

2. SOLUTION

Checking the website with wget,

$ wget https://www.example.com
--2018-01-14 16:58:36--  https://www.example.com/
Resolving www.example.com (www.example.com)... 198.51.100.12, 2001:db8:1221:2341:f03c:f27b:12fa:2123
Connecting to www.example.com (www.example.com)|198.51.100.12|:443... connected.ERROR: cannot verify www.example.com's certificate, issued by ‘CN=Typical Encryption Authority X3,O=Typical Encryption,C=XX’:
  Issued certificate ...

1.0 Exif metadata not preserved by image editing program

Problem: After an image is developed and edited by image editing software and saved in a format like JPEG, it does not have the Exif metadata.

2.0 Solution

Surprisingly, quite a few image editing programs do not preserve the Exif metadata of images and attempts ...

1.0 Adding the IPTC metadata

After a photograph has been taken and processed, it might be necessary to add IPTC metadata before it can be published. If your image editing software does not support adding of IPTC metadata to the image, you can accomplish this is by using the exiv2 command ...

1.0 π

While using bc for calculations, the value of π is sometimes required. Sure, you might remember it as 3.1416, but it is better to use a higher precision value. And it's quite simple to do that.

First, we need to start bc with the option

1.0 Error

While executing the dig command, the sendmsg() failed: Operation not permitted error was printed.

$ dig example.com
../../../../lib/isc/unix/net.c:581: sendmsg() failed: Operation not permitted
../../../../lib/isc/unix/net.c:581: sendmsg() failed: Operation not permitted
...

2.0 Solution

The error was resolved after adding the following iptables rules.

iptables -I OUTPUT 1 -p udp -s ...

1.0 Introduction

Given an nginx web server log file, we might like to know who are the visitors to our website. One can go line by line through the log file, but that is tedious. It would be nice if we can get one line per client visiting the website, giving the IP ...

1.0 Error

A signed APK of an Android app was built using the Android Studio. When we tried to download the signed APK to a device using the adb command, the command failed with the error, INSTALL_PARSE_FAILED_NO_CERTIFICATES.

$ adb install app-release.apk 
app-release.apk: ...

1.0 Error

While trying to open sitemap.xml of a site served by nginx and built using Drupal CMS, the 404 Not Found error was received. The nginx log file, error.log gave the error as, 80 open() sitemap.xml failed (2: No such file or directory).

2.0 ...

1.0 Error

While running optipng on a png file, the following error was obtained,

Error: Can't back up the existing output file

2.0 Solution

The file was not having the write permission. Once, the write mode bit for the file was set, optipng worked fine.

$ ls -ls ...

1.0 Scenario

While searching on a topic, you land up on a GitHub page with code. The code looks interesting. But you can not work on it on GitHub. You need to get it on your computer to work on it. How to get it on your computer?

2.0 Solution: Get the repository

The code displayed on the ...