The following exception is caused by a lack of memory and not having swap

Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-for details

http://www.linuxidc.com/Linux/2010-09/28915.htm ubuntu增加交换空间的步骤

提供了创建交换空间的方法

proc_open(): fork failed errors#

If composer shows proc_open() fork failed on some commands:

PHP Fatal error: Uncaught exception 'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar

This could be happening because the VPS runs out of memory and has no Swap space enabled.

free-mtotal used free shared buffers cachedMem:2048357169000237-/+ buffers/cache:1191928Swap:000

To enable the swap you can use for example:

/bin/ddif=/dev/zero of=/var/swap.1 bs=1M count=1024/sbin/mkswap/var/swap.1/sbin/swapon/var/swap.1

下面是整个过程

root@tyr:/var/www/html/laravel#./composer.phar global require "laravel/installer=~1.1"Changedcurrentdirectory to /root/.composer

PHP Fatal error:  Call to undefined method Fxp\Composer\AssetPlugin\Package\Version\VersionParser::parseLinks() in /root/.composer/vendor/fxp/composer-asset-plugin/Repository/VcsPackageFilter.php on line 272Fatal error: Call to undefined method Fxp\Composer\AssetPlugin\Package\Version\VersionParser::parseLinks() in /root/.composer/vendor/fxp/composer-asset-plugin/Repository/VcsPackageFilter.php on line 272root@tyr:/var/www/html/laravel#composer require "fxp/composer-asset-plugin:~1.0"./composer.json has been created

Loading composer repositories with package information

Updating dependencies (includingrequire-dev)- Installing fxp/composer-asset-plugin (v1.0.3)

Downloading: 100%The followingexceptionis caused by a lack of memory and not having swap configured

Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for detailsPHP Fatal error:  Uncaughtexception'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php:974Stack trace:#0 [internal function]: Composer\Util\ErrorHandler::handle(2, 'proc_open(): fo...', 'phar:///usr/loc...', 974, Array)#1 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(974): proc_open('stty -a | grep ...', Array, NULL, NULL, NULL, Array)#2 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(784): Symfony\Component\Console\Application->getSttyColumns()#3 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(745): Symfony\Component\Console\Application->getTerminalDimensions()#4 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(675): Symfony\Component\Console\Application->getTerminalWidth()#5 phar:///usr/local/bin/com in phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php on line 974Fatal error: Uncaughtexception'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php:974Stack trace:#0 [internal function]: Composer\Util\ErrorHandler::handle(2, 'proc_open(): fo...', 'phar:///usr/loc...', 974, Array)#1 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(974): proc_open('stty -a | grep ...', Array, NULL, NULL, NULL, Array)#2 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(784): Symfony\Component\Console\Application->getSttyColumns()#3 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(745): Symfony\Component\Console\Application->getTerminalDimensions()#4 phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php(675): Symfony\Component\Console\Application->getTerminalWidth()#5 phar:///usr/local/bin/com in phar:///usr/local/bin/composer/vendor/symfony/console/Symfony/Component/Console/Application.php on line 974root@tyr:/var/www/html/laravel#free -mtotal      used      free    shared    buffers    cached

Mem:          488        414        74        24          1        71-/+ buffers/cache:        340        147Swap:            0          0          0root@tyr:/var/www/html/laravel#/bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=10241024+0records in1024+0records out1073741824 bytes (1.1 GB) copied, 25.3413 s, 42.4 MB/s

root@tyr:/var/www/html/laravel#/sbin/mkswap /var/swap.1Setting up swapspace version 1, size = 1048572KiB

no label, UUID=60a9b908-925a-4161-8fca-7ae2d5a76154

root@tyr:/var/www/html/laravel#/sbin/swapon /var/swap.1root@tyr:/var/www/html/laravel#free -mtotal      used      free    shared    buffers    cached

Mem:          488        474        13        24          2        127-/+ buffers/cache:        344        143Swap:        1023          0      1023root@tyr:/var/www/html/laravel#composer require "fxp/composer-asset-plugin:~1.0"./composer.json has been updated

Loading composer repositories with package information

Updating dependencies (includingrequire-dev)- Installing fxp/composer-asset-plugin (v1.0.3)

Loading from cache

Writing lockfileGenerating autoload files

root@tyr:/var/www/html/laravel#