I've got a little issue here regarding autoconf. Basically I did this:

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[root@www bin]# cd /opt
[root@www opt]# wget http://pecl.php.net/get/memcache-2.1.0.tgz
--10:41:02-- http://pecl.php.net/get/memcache-2.1.0.tgz
=> `memcache-2.1.0.tgz'
Resolving pecl.php.net... 216.92.131.66
Connecting to pecl.php.net|216.92.131.66|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 19,567 (19K) [application/octet-stream]

100%[==================================================================================================== ===================================>] 19,567 92.76K/s

10:41:02 (92.49 KB/s) - `memcache-2.1.0.tgz' saved [19567/19567]

[root@www opt]# gunzip memcache-2.1.0.tgz
[root@www opt]# tar -xvf memcache-2.1.0.tar
package.xml
memcache-2.1.0/CREDITS
memcache-2.1.0/README
memcache-2.1.0/example.php
memcache-2.1.0/config.m4
memcache-2.1.0/config.w32
memcache-2.1.0/php_memcache.h
memcache-2.1.0/memcache.c
memcache-2.1.0/memcache.dsp
[root@www opt]# cd memcache-2.1.0
[root@www memcache-2.1.0]# ls
config.m4 config.w32 CREDITS example.php memcache.c memcache.dsp php_memcache.h README
[root@www memcache-2.1.0]# phpize
Configuring for:
PHP Api Version: 20041225
Zend Module Api No: 20060613
Zend Extension Api No: 220060519
Cannot find autoconf. Please check your autoconf installation and the $PHP_AUTOCONF
environment variable is set correctly and then rerun this script.
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I've found autoconf and did:

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[root@www memcached-1.2.4]# export PHP_AUTOCONF="/usr/bin/"
[root@www memcached-1.2.4]# pecl install memcache
downloading memcache-2.2.3.tgz ...
Starting to download memcache-2.2.3.tgz (27,304 bytes)
.........done: 27,304 bytes
11 source files, building
running: phpize
Configuring for:
PHP Api Version: 20041225
Zend Module Api No: 20060613
Zend Extension Api No: 220060519
/usr/bin/phpize: /tmp/pear/cache/memcache-2.2.3/build/shtool: /bin/sh: bad interpreter: Permission denied
Cannot find autoconf. Please check your autoconf installation and the $PHP_AUTOCONF
environment variable is set correctly and then rerun this script.

ERROR: `phpize' failed
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I'm not 100% sure what I should change $PHP_AUTOCONF to. Any ideas?

Aw, come on. No one knows?

> /usr/bin/phpize: /tmp/pear/cache/memcache-2.2.3/build/shtool: /bin/sh: bad interpreter: Permission denied

You probably know by now, but others like me might still be looking for the answer...

Check that you can execute scripts out of the /tmp directory. E.g. on my system:

# mount -l | grep /tmp
/dev/sda2 on /tmp type ext3 (rw,noexec,nosuid,nodev) [/tmp]

I remounted /tmp without the noexec flag and then the install worked.

Another option for those who can't remount /tmp should be to use a different temporary directory.

# pear config-set temp_dir /var/tmp/pear/temp
config-set succeeded

The above comment to remount the tmp file by making it executable definitely did the job for me!

Just a little more help to others reading this. To remount the tmp directory, just use:
# mount -o remount,exec /tmp

And after you are done with the installation, for security purpose, run:
# mount -o remount,noexec /tmp

Cheers!

Cubix Web Solutions