Coding Life: April 2019

Method 1: Reconfigure Package Database

The first method you can try is to reconfigure the package database. Probably the database got corrupted while installing a package. Reconfiguring often fixes the problem.

sudo dpkg --configure -a

Method 2: Use force install

If a package installation was interrupted previously, you may try to do a force install.

sudo apt-get install -f

Method 3: Try removing the troublesome package

If it’s not an issue for you, you may try to remove the package manually. Please don’t do it for Linux Kernels (packages starting with linux-).

sudo apt remove

Method 4: Remove post info files of the troublesome package

This should be your last resort. You can try removing the files associated to the package in question from /var/lib/dpkg/info. for example the package name is "desktop-base"

ls -l /var/lib/dpkg/info | grep -i desktop-base

sudo rm -rf /var/lib/dpkg/info/desktop-base*

Use the sudo apt update and then you should be able to install software as usual.

reference article: https://itsfoss.com/dpkg-returned-an-error-code-1/

Using the mailx command

Once installed, the mailx command can be directly referenced with the name mail, so you just type in that in the command line.

1. Simple mail

Run the following command, and then mailx would wait for you to enter the message of the email. You can hit enter for new lines. When done typing the message, press Ctrl+D and mailx would display EOT.
After than mailx automatically delivers the email to the destination.

$ mail -s "This is the subject" someone@example.com
Hi someone
How are you
I am fine
Bye
EOT

2. Take message from a file

The message body of the email can be taken from a file as well.

$ mail -s "This is Subject" someone@example.com < /path/to/file

The message can also be piped using the echo command -

$ echo "This is message body" | mail -s "This is Subject" someone@example.com

3. Multiple recipients

To send the mail to multiple recipients, specify all the emails separated by a comma

$ echo "This is message body" | mail -s "This is Subject" someone@example.com,someone2@example.com

4. CC and BCC

The "-c" and "-b" options can be used to add CC and BCC addresses respectively.

$ echo "This is message body" | mail -s "This is Subject" -c ccuser@example.com someone@example.com

5. Specify From name and address

To specify a "FROM" name and address, use the "-r" option. The name should be followed by the address wrapped in "<>".

$ echo "This is message body" | mail -s "This is Subject" -r "Harry" someone@example.com

6. Specify "Reply-To" address

The reply to address is set with the internal option variable "replyto" using the "-S" option.

# replyto email
$ echo "This is message" | mail -s "Testing replyto" -S replyto="mark@gmail.com" someone@example.com

# replyto email with a name
$ echo "This is message" | mail -s "Testing replyto" -S replyto="Mark" someone@example.com

7. Attachments

Attachments can be added with the "-a" option.

$ echo "This is message body" | mail -s "This is Subject" -r "Harry" -a /path/to/file someone@example.com

8. Use external SMTP server

This is an exclusive feature, that you get only with heirloom mailx and not bsd mailx, or the mail command from gnu mailutils or the mutt command.
The mailx command can use an external smtp server to use to relay the message forward. The syntax is a bit lengthy but makes sense.

$ echo "This is the message body and contains the message" | mailx -v -r "someone@example.com" -s "This is the subject" -S smtp="mail.example.com:587" -S smtp-use-starttls -S smtp-auth=login -S smtp-auth-user="someone@example.com" -S smtp-auth-password="abc123" -S ssl-verify=ignore yourfriend@gmail.com

Here is a breakdown

$ echo "This is the message body and contains the message" | mailx -v \
> -r "someone@example.com" \
> -s "This is the subject" \
> -S smtp="mail.example.com:587" \
> -S smtp-use-starttls \
> -S smtp-auth=login \
> -S smtp-auth-user="someone@example.com" \
> -S smtp-auth-password="abc123" \
> -S ssl-verify=ignore \
> yourfriend@gmail.com

You can use the gmail smtp servers and send emails via your gmail account. That is so cool!
For gmail specifically you would need to enable less secure apps settings before you can send mail like that.

9. Verbose - watch smtp communication

When using external smtp servers, you can choose to watch the entire smtp communication that is done in the background. This is useful specially when testing or debugging smtp servers.

$ echo "This is the message body and contains the message from heirloom mailx" | mailx -v -s "This is the subject" -S smtp="smtp.gmail.com:587" -S smtp-use-starttls -S smtp-auth=login -S smtp-auth-user="mygmail@gmail.com" -S smtp-auth-password="mypassword" -S ssl-verify=ignore someone@example.com
Resolving host smtp.gmail.com . . . done.
Connecting to 74.125.68.109:587 . . . connected.
220 mx.google.com ESMTP je4sm32812877pbd.94 - gsmtp
>>> EHLO enlightened
250-mx.google.com at your service, [122.163.43.21]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
>>> STARTTLS
220 2.0.0 Ready to start TLS
>>> EHLO enlightened
250-mx.google.com at your service, [122.163.43.21]
250-SIZE 35882577
250-8BITMIME
250-AUTH LOGIN PLAIN XOAUTH XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
>>> AUTH LOGIN
334 VXNlcmU6
>>> YmnbWFpbC5jb20=
334 UGFzcmQ6
>>> KnJgzKg==
235 2.7.0 Accepted
>>> MAIL FROM:
250 2.1.0 OK je4sm32812877pbd.94 - gsmtp
>>> RCPT TO:
250 2.1.5 OK je4sm32812877pbd.94 - gsmtp
>>> DATA
354  Go ahead je4sm32812877pbd.94 - gsmtp
>>> .
250 2.0.0 OK 1417930703 je4sm32812877pbd.94 - gsmtp
>>> QUIT
221 2.0.0 closing connection je4sm32812877pbd.94 - gsmtp

Troubleshooting

In case the mails are not being delivered properly you need to check a few things. The first thing to check is that an smtp server (mta) is running locally. The netstat command can tell that

$ sudo netstat -ltnp | grep 25
[sudo] password for enlightened: 
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      2541/master     
tcp6       0      0 :::25                   :::*                    LISTEN      2541/master

If an stmp server like Postfix is running and still mails are not going, then try re-configuring Postfix for example. On Ubuntu/Debian systems, this can be done with the dpkg-reconfigure command

```
$ sudo dpkg-reconfigure postfix
```

Then retry, the mail command and it should work. If it still doesn't, try contacting your server provider.

No mails from local systems
If you try to send mails from your local computer to a gmail address, your mail would most likely be rejected, so don't try doing that.

This is because ordinary computers connected to internet address have an ip address that is not associated with any valid domain as such, and gmail strictly verifies such credentials before approving any mail to go through.

Notes and Resources

Apart from mailx, there are other tools like Swaks and smtp-cli that can be used to send mails from command line and support various features like specifying smtp servers and adding attachments and so on.

However the mailx command is available in the default repositories of most common distros, so can be installed easily. Further it maintains a syntax very similar to that of the mail command which makes it a drop in replacement for the older mail command.

The mailx command is even capable of reading mails from remote IMAP servers, but that is something we kept out of this post and would talk later. To learn more check the man page for the mailx command with "man mailx".

Article source: https://www.binarytides.com/linux-mailx-command/

Coding Life

xrdp shows blank screen on ubuntu 16.04

Installing the xfce4 Desktop environment

Configure xrdp to use xfce desktop environment

Test your xrdp connection

How to resolve "Sub-process /usr/bin/dpkg returned an error code (1)"