Como declarado no Manual do Pear e também explicou o mesmo aqui , é Diretório de download do PEAR Installer .
$ pear config-show
Configuration (channel pear.php.net):
=====================================
Auto-discover new Channels auto_discover <not set>
Default Channel default_channel pear.php.net
HTTP Proxy Server Address http_proxy <not set>
PEAR server [DEPRECATED] master_server pear.php.net
Default Channel Mirror preferred_mirror pear.php.net
Remote Configuration File remote_config <not set>
PEAR executables directory bin_dir /usr/bin
PEAR documentation directory doc_dir /usr/share/php/doc
PHP extension directory ext_dir /usr/lib/php5/20090626+lfs
PEAR directory php_dir /usr/share/php
PEAR Installer cache directory cache_dir /tmp/pear/cache
PEAR configuration file cfg_dir /usr/share/php/cfg
directory
PEAR data directory data_dir /usr/share/php/data
PEAR Installer download download_dir /build/buildd/php5-5.3.6/pear-build-download
directory
PHP CLI/CGI binary php_bin /usr/bin/php
php.ini location php_ini <not set>
--program-prefix passed to php_prefix <not set>
PHP's ./configure
--program-suffix passed to php_suffix <not set>
PHP's ./configure
PEAR Installer temp directory temp_dir /tmp/pear/temp
PEAR test directory test_dir /usr/share/php/test
PEAR www files directory www_dir /usr/share/php/htdocs
Cache TimeToLive cache_ttl 3600
Preferred Package State preferred_state stable
Unix file mask umask 2
Debug Log Level verbose 1
PEAR password (for password <not set>
maintainers)
Signature Handling Program sig_bin /usr/bin/gpg
Signature Key Directory sig_keydir /etc/pear/pearkeys
Signature Key Id sig_keyid <not set>
Package Signature Type sig_type gpg
PEAR username (for username <not set>
maintainers)
User Configuration File Filename /home/cb/.pearrc
System Configuration File Filename /etc/pear/pear.conf