When running Jenkins CI on a 1GB VPS (Virtual Private Server), you might encounter the frustrating error:

java.io.IOException: Cannot run program "/usr/bin/env": 
java.io.IOException: error=12, Cannot allocate memory

This typically occurs during build steps like Ant/Maven execution, even when the system shows available memory. Here's why this happens and how to fix it.

The error occurs because Linux kernel's overcommit memory policy prevents processes from allocating memory even when theoretically available. On constrained VPS environments like HostEurope's 1GB plan, this becomes particularly problematic when:

• Multiple Java processes run simultaneously (Jenkins master + build tools)
• Default Java heap sizes are too aggressive
• System has minimal swap space configured

1. Optimize Java Heap Settings

Edit Jenkins configuration (typically /etc/default/jenkins):

# Set conservative heap sizes
JAVA_ARGS="-Xms256m -Xmx512m -XX:MaxRAM=768m"
# Add aggressive garbage collection
JAVA_ARGS="$JAVA_ARGS -XX:+UseG1GC -XX:+UseStringDeduplication"
# Limit permgen/metaspace
JAVA_ARGS="$JAVA_ARGS -XX:MaxMetaspaceSize=128m"

2. Configure Build-Specific Memory

For Ant builds, create a jenkins-ant-wrapper.sh:

#!/bin/bash
export ANT_OPTS="-Xmx256m -XX:MaxRAM=384m"
exec ant "$@"

Then configure your Jenkins job to use this wrapper:

#!/bin/bash
/path/to/jenkins-ant-wrapper.sh clean build

3. System-Level Tweaks

Add swap space if none exists (1GB recommended for 1GB RAM):

sudo fallocate -l 1G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo echo "/swapfile swap swap defaults 0 0" >> /etc/fstab

If you frequently build memory-intensive projects:

• Upgrade to at least 2GB RAM VPS
• Consider separating build agents from Jenkins master
• For Java-heavy builds, monitor actual usage with:

watch -n 5 free -m

For Jenkins pipeline projects, declare memory constraints directly in Jenkinsfile:

pipeline {
    agent any
    environment {
        ANT_OPTS = "-Xmx192m -XX:MaxRAM=256m"
    }
    stages {
        stage('Build') {
            steps {
                sh 'ant -f build.xml'
            }
        }
    }
}

Install the Monitoring Plugin to track:

• JVM heap usage
• Thread counts
• GC activity

Configure system monitoring with:

sudo apt install htop
htop

---

When running Jenkins CI on memory-constrained virtual servers (like HostEurope's 1GB dynamic instances), developers often encounter the dreaded "Cannot allocate memory" error during builds. This typically manifests when Java processes (either Jenkins itself or build tools like Ant) attempt to allocate more memory than the system can provide.

The error message java.io.IOException: error=12, Cannot allocate memory indicates the OS is preventing process creation due to memory constraints. In VPS environments, there are three potential bottlenecks:

# Check available memory
free -m

# Check Java process limits
ps aux | grep java

# Check system-wide memory limits
cat /proc/meminfo | grep MemTotal

For a 1GB server running both Jenkins and build tools, these configurations work best:

# Jenkins JVM settings (/etc/default/jenkins)
JAVA_ARGS="-Xms256m -Xmx512m -XX:MaxPermSize=128m"

# Ant environment variables (~/.bashrc or build script)
export ANT_OPTS="-Xmx128m -Xms64m -XX:MaxPermSize=64m"

Consider these architectural improvements:

# Sample Jenkinsfile configuration for memory efficiency
pipeline {
    agent any
    options {
        timeout(time: 30, unit: 'MINUTES')
        disableConcurrentBuilds()
    }
    stages {
        stage('Build') {
            steps {
                script {
                    // Run memory-intensive steps in isolated processes
                    sh 'ant -Dbuild.compiler=modern -f build.xml clean compile'
                }
            }
        }
    }
}

When persistent memory issues occur:

1. Use Jenkins agents to offload builds to separate machines
2. Implement build tool wrappers to enforce memory limits:

#!/bin/bash
# build-wrapper.sh
MEM_LIMIT=128m
JAVA_TOOL_OPTIONS="-Xmx${MEM_LIMIT}" ant "$@"