How can I solve “E: Package ‘php-mcrypt’ has no installation candidate” on Ubuntu 20.04/18.04?. Today’s guide will be on the installation of PHP mcrypt extension on Ubuntu 20.04/18.04. The PHP mcrypt extension is an interface to the mcrypt cryptography library and it supports a wide variety of block algorithms such as DES, TripleDES, Blowfish (default), 3-WAY, SAFER-SK64, SAFER-SK128, TWOFISH, TEA, RC2 and GOST in CBC, OFB, CFB and ECB cipher modes.

If you try installing mcrypt with apt you’ll get an error:

$ sudo apt update
$ sudo apt install php-mcrypt
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package php-mcrypt is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'php-mcrypt' has no installation candidate

The mcrypt extension was moved to the PECL repository and is no longer bundled with PHP as of PHP 7.2.0. PECL is a repository for all known PHP extensions where users can download and host developed PHP extensions.

Tell your OS to pull the latest list of packages available in repositories for installation:

sudo apt update

Install Development tools on Ubuntu:

sudo apt install -y build-essential

Confirm make and gcc:

$ gcc --version
gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ make --version
GNU Make 4.2.1
Built for x86_64-pc-linux-gnu
Copyright (C) 1988-2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

You’ll need to first install PHP, dev and pear extensions on Ubuntu 20.04|18.04.

sudo apt install php php-pear php-dev libmcrypt-dev

Confirm pecl command is available in your system.

$ which pecl 
/usr/bin/pecl

PECL usage:

$ pecl help
Commands:
build                  Build an Extension From C Source
bundle                 Unpacks a Pecl Package
channel-add            Add a Channel
channel-alias          Specify an alias to a channel name
channel-delete         Remove a Channel From the List
channel-discover       Initialize a Channel from its server
channel-info           Retrieve Information on a Channel
channel-login          Connects and authenticates to remote channel server
channel-logout         Logs out from the remote channel server
channel-update         Update an Existing Channel
clear-cache            Clear Web Services Cache
config-create          Create a Default configuration file
config-get             Show One Setting
config-help            Show Information About Setting
config-set             Change Setting
config-show            Show All Settings
convert                Convert a package.xml 1.0 to package.xml 2.0 format
cvsdiff                Run a "cvs diff" for all files in a package
cvstag                 Set CVS Release Tag
download               Download Package
download-all           Downloads each available package from the default channel
info                   Display information about a package
install                Install Package
list                   List Installed Packages In The Default Channel
list-all               List All Packages
list-channels          List Available Channels
list-files             List Files In Installed Package
list-upgrades          List Available Upgrades
login                  Connects and authenticates to remote server [Deprecated in favor of channel-login]
logout                 Logs out from the remote server [Deprecated in favor of channel-logout]
makerpm                Builds an RPM spec file from a PEAR package
package                Build Package
package-dependencies   Show package dependencies
package-validate       Validate Package Consistency
pickle                 Build PECL Package
remote-info            Information About Remote Packages
remote-list            List Remote Packages
run-scripts            Run Post-Install Scripts bundled with a package
run-tests              Run Regression Tests
search                 Search remote package database
shell-test             Shell Script Test
sign                   Sign a package distribution file
svntag                 Set SVN Release Tag
uninstall              Un-install Package
update-channels        Update the Channel List
upgrade                Upgrade Package
upgrade-all            Upgrade All Packages [Deprecated in favor of calling upgrade with no parameters]
Usage: pecl [options] command [command-options] <parameters>
Type "pecl help options" to list all options.
Type "pecl help shortcuts" to list all command shortcuts.
Type "pecl help version" or "pecl version" to list version information.
Type "pecl help <command>" to get the help for the specified command.

Update channels:

$ sudo pecl channel-update pecl.php.net
Updating channel "pecl.php.net"
Update of Channel "pecl.php.net" succeeded

$ sudo pecl update-channels
Updating channel "doc.php.net"
Update of Channel "doc.php.net" succeeded
Updating channel "pear.php.net"
Update of Channel "pear.php.net" succeeded
Updating channel "pecl.php.net"
Channel "pecl.php.net" is up to date

Let’s search for mcrypt extension.

$ sudo pecl search mcrypt
Matched packages, channel pecl.php.net:
=======================================
Package       Stable/(Latest) Local
mcrypt        1.0.4 (stable)        Bindings for the libmcrypt library
mcrypt_filter 0.1.0 (beta)          Applies mcrypt symmetric encryption using stream filters

You can the install mcrypt extension using pecl command with install option.

$ sudo pecl install mcrypt
downloading mcrypt-1.0.4.tgz ...
Starting to download mcrypt-1.0.4.tgz (27,056 bytes)
.........done: 27,056 bytes
6 source files, building
running: phpize
Configuring for:
PHP Api Version:         20190902
Zend Module Api No:      20190902
Zend Extension Api No:   320190902
........

When you see a prompt

libmcrypt prefix? [autodetect] :

Press Enter to autodetect.

You should get an output like below for completed installation of mcrypt extension on Ubuntu 20.04 Linux machine.

Build process completed successfully
Installing '/usr/lib/php/20190902/mcrypt.so'
install ok: channel://pecl.php.net/mcrypt-1.0.4
configuration option "php_ini" is not set to php.ini location
You should add "extension=mcrypt.so" to php.ini

Enable extension in php.ini file. You can use nano or vim editor:

$ sudo vim /etc/php/*/cli/php.ini
extension=mcrypt.so

$ sudo vim /etc/php/*/apache2/php.ini
extension=mcrypt.so

You can confirm that the module was installed and enabled with the command:

$ php -m | grep mcrypt
mcrypt

If using an application hosted with an Apache or Nginx web server restart them.

### Restart Apache web server ###
sudo systemctl restart apache2

### Restart nginx web server ###
sudo systemctl restart nginx

And that’s how you can easily install mcrypt PHP extension on Ubuntu 20.4 & Ubuntu 18.04 Linux system.