How to Preserve Environment Variables When Starting Services with Linux service Command


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When working with the service command in Linux, many administrators encounter unexpected behavior regarding environment variables. The manual page explicitly states:

service runs a System V init script in as predictable environment as possible,
removing most environment variables and with current working directory set to /.

This behavior is intentional to create a clean, predictable environment for service execution. However, it can cause issues when your service relies on specific environment variables.

The typical approaches that don't work include:

  • Setting variables in /etc/profile.d/ or ~/.bashrc
  • Exporting variables in the shell before running service
  • Using source commands in the init script

Method 1: Using /etc/default Files

Many services support reading configuration from /etc/default/[servicename]:

# /etc/default/myservice
export MY_VAR="/path/to/required/directory"

Then modify your init script to source this file:

# /etc/init.d/myservice
[ -f /etc/default/myservice ] && . /etc/default/myservice

Method 2: Systemd EnvironmentFile Directive

For systems using systemd (most modern distributions):

# /etc/systemd/system/myservice.service
[Service]
EnvironmentFile=/etc/sysconfig/myservice
ExecStart=/usr/bin/myservice

Create the environment file:

# /etc/sysconfig/myservice
MY_VAR="/path/to/required/directory"

Method 3: Direct Modification of Init Script

For legacy systems where other methods aren't feasible:

# /etc/init.d/myservice
# Add near the top of the file
export MY_VAR="/path/to/required/directory"
  • Security: Environment variables in /etc/default files should have restricted permissions (640 root:root)
  • Portability: The /etc/default method works across most Linux distributions
  • Maintainability: Separate configuration from init scripts for easier updates

To verify your environment is properly configured:

# Add to your init script before the service starts
env > /tmp/service-env.log

This will create a log file showing exactly what environment the service sees during startup.

When working with System V init scripts on Linux, many developers encounter this frustrating scenario: environment variables set in /etc/profile.d/ or shell configurations mysteriously disappear when starting services via the service command. This behavior is actually documented in the man pages - the service command intentionally strips most environment variables to create a clean, predictable execution environment.

# Example of the issue
$ export MY_APP_PATH=/opt/myapp
$ service myapp start  # MY_APP_PATH won't be available

The service wrapper does several things that affect environment variables:

  • Changes working directory to /
  • Removes most inherited environment variables
  • Only preserves a minimal set (PATH, TERM, LANG, etc.)
  • Runs scripts with env -i for clean environment

1. Modify the init script directly

The most straightforward approach is to edit the init script to include required variables:

# /etc/init.d/myapp
#!/bin/sh

# Add variables at the top
export MY_APP_PATH=/opt/myapp
export CONFIG_FILE=/etc/myapp.conf

# Rest of init script...

2. Use systemd service files (modern systems)

For systems using systemd, create or modify the service unit file:

# /etc/systemd/system/myapp.service
[Unit]
Description=My Application

[Service]
Environment="MY_APP_PATH=/opt/myapp"
Environment="CONFIG_FILE=/etc/myapp.conf"
ExecStart=/usr/bin/myapp
Restart=on-failure

[Install]
WantedBy=multi-user.target

3. Create a wrapper script

For systems where you can't modify the init script:

# /usr/local/bin/myapp-wrapper
#!/bin/bash
export MY_APP_PATH=/opt/myapp
export CONFIG_FILE=/etc/myapp.conf
exec /etc/init.d/myapp-original "$@"

# Then update service to point to the wrapper

When choosing a solution, consider:

  • Security implications of environment variables
  • Maintainability across updates
  • Portability between systems
  • Need for variable substitution (e.g., using $HOME)

For sensitive values, consider using configuration files instead of environment variables, or use tools like envdir for more controlled variable management.