[root@web1 ~]# pecl install apc
downloading APC-3.1.9.tgz ...
Starting to download APC-3.1.9.tgz (155,540 bytes)
.................................done: 155,540 bytes
54 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/temp/APC/build/shtool: /bin/sh: bad interpreter: Permission denied
Cannot find autoconf. Please check your autoconf installation and the
$PHP_AUTOCONF environment variable. Then, rerun this script.

ERROR: `phpize' failed

The problem is caused by the /tmp/ filesystem being mounted noexec, which keeps any programs on /tmp/ from being allowed to be executed, which breaks the install script.

To remount /tmp/ as executable, use:

[root@web1 ~]# mount -o remount,exec,suid /tmp

The it should install correctly.

After the install is done, remount the /tmp/ filesystem with the noexec permissions reset.

[root@web1 ~]# mount -o remount,noexec,nosuid /tmp