Composer proc_open(): fork failed - Cannot allocate memory - out-of-memory

Question

I have this same error as others when running php ~/composer.phar update:
The following exception is 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 details
Fatal error: Uncaught exception 'ErrorException' with message 'proc_open(): fork failed - Cannot allocate memory' in phar:///home/tea/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php:974
Stack trace:
0 [internal function]: Composer\Util\ErrorHandler::handle(2, 'proc_open(): fo...', 'phar:///home/te...', 974, Array)
1 phar:///home/tea/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php(974): proc_open('stty -a | grep ...', Array, NULL, NULL, NULL, Array)
2 phar:///home/tea/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php(784): Symfony\Component\Console\Application->getSttyColumns()
3 phar:///home/tea/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php(745): Symfony\Component\Console\Application->getTerminalDimensions()
4 phar:///home/tea/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php(675): Symfony\Component\Console\Application->getTerminalWidth()
5 phar:///home/tea/composer in phar:///home/tea/composer.phar/vendor/symfony/console/Symfony/Component/Console/Application.php on line 974
...but with a large instance: 4gb RAM and 4gb swap. The free RAM is never exhausted, let alone the available/cached RAM, and the swap isn't touched!
total used free shared buff/cache available
Mem: 3788 885 1908 9 993 2692
Swap: 3967 0 3967
It's the first time running composer update on this new machine, CentOS/CloudLinux 7.1 (with cPanel).
In desperation, I've tried
# php -dmemory_limit=1G ../composer.phar update --no-scripts --prefer-dist
and I've tried removing the composer.lock and vendor files and even tried adding a temporary swap file but it really doesn't seem to be a memory problem - could the error be misguided?
proc_open is not disabled and I also tried with shell fork bomb protection disabled but no jive.
Would love a heads up.
N.B. I'm aware of the advice to commit the composer.lock file and do a composer install but this instance is being used for dev (as was the previous CentOS/CloudLinux 6.x machine with smaller resource specs) so we need to use the same methods we were using previously.

Answer 1

OK so it was CloudLinux limiting the memory for the user to 1024mb, because it works when the limit is doubled to 2048mb.
That's the same setting on our previous server (CentOS/CloudLinux 6.x) but it looks like each version of CentOS is much more memory hungry than the rest.
Whats weird is that running composer with --profile shows the most it uses is 482mb. Even if it doubles when forking (as has been suggested) that's still below the 1024mb limit.

Answer 2

I ran into the same problem. My system had 1.5GB RAM free and it was not enough...Composer was eating too much memory very fast.
My only solution was to clear cache and update to latest version (1.4.2):
composer clear-cache
sudo composer selfupdate

Answer 3

That happens when you have low memory resources and you don't have swap enabled, i had the same problem and fixed using this few commands bellow, or you can create a swap partition or file, just make sure that you activate swap.
$ /bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
$ /sbin/mkswap /var/swap.1
$ /sbin/swapon /var/swap.1
I hope it works for you...