Composer: 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 -m
 
total used free shared buffers cached
Mem: 2048 357 1690 0 0 237
-/+ buffers/cache: 119 1928
Swap: 0 0 0
 
# To enable the swap you can use for example
/bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
/sbin/mkswap /var/swap.1
/sbin/swapon /var/swap.1