Complete Guide to Viewing and Managing Boot Startup Items in CentOS/RHEL Systems

Understanding Linux Runlevels and Startup Items

Linux systems define 7 runlevels to control which services start in different system states:

• 0: Halt (Shutdown)
• 1: Single-user mode (Rescue mode)
• 2: Multi-user mode without networking (typically unused)
• 3: Full multi-user text mode (common for servers)
• 4: Reserved (typically unused)
• 5: Graphical interface mode (common for desktops)
• 6: Reboot

To view the startup status of all services across runlevels, use the chkconfig --list command.

Managing Service Startup Status with chkconfig

chkconfig is the primary tool for managing SysV init services in CentOS/RHEL 6 and earlier versions. Basic syntax:

# View service status
chkconfig --list [service_name]

# Enable/disable service at specific runlevels
chkconfig --level [levels] [service_name] {on|off}

# Add or remove service from management
chkconfig --add [service_name]
chkconfig --del [service_name]

Example: Managing SSH Service

To disable sshd service at runlevels 3 and 5:

chkconfig --level 35 sshd off

To verify the change:

chkconfig --list sshd

Manually Managing Startup Script Directories

Besides chkconfig, you can directly manage files in the /etc/rc.d/ directory.

# View /etc/rc.d/ structure
ls /etc/rc.d/

# Example output (CentOS 6):
# init.d rc0.d rc1.d rc2.d rc3.d rc4.d rc5.d rc6.d rc.local rc.sysinit

• init.d/: Contains all service startup scripts.
• rcN.d/ (N=0~6): Symbolic link directories for each runlevel.
• rc.local: Custom startup script executed last.
• rc.sysinit: System initialization script.

Understanding Files in rcN.d Directories

Example for rc3.d/ (runlevel 3):

ls /etc/rc.d/rc3.d/

# Example output:
# K02avahi-dnsconfd S25bluetooth
# K02NetworkManager S25netfs
# S04readahead_early S26apmd

• K prefix: Services to stop when entering this runlevel. Numbers indicate execution order.
• S prefix: Services to start when entering this runlevel. Numbers indicate execution order.

Important rule: System executes all K (Kill) scripts first in numerical order, then all S (Start) scripts. Thus, S script startup commands override K script stop commands for the same service.

Common Methods to Set Programs for Automatic Startup

To make vncserver start automatically after boot, here are several methods.

Method 1: Register Program as System Service (Recommended)

This is the most standard method for long-running daemons.

1. Check service status:

   chkconfig --list | grep vnc

2. Enable at boot (e.g., at runlevel 5):

   chkconfig --level 5 vncserver on

3. Verify:

   chkconfig --list | grep vnc
   # Output should show: vncserver 0:off ... 5:on 6:off

Method 2: Using /etc/rc.local Script

/etc/rc.local runs last after all initialization scripts. Suitable for simple startup commands.

# Edit rc.local file
vi /etc/rc.local

# Add your command before 'exit 0', e.g.:
/usr/bin/vncserver :1

# Ensure rc.local is executable
chmod +x /etc/rc.local

Method 3: Create Custom Systemd Service (CentOS/RHEL 7+)

Note: CentOS/RHEL 7+ uses systemd instead of SysV init. Updated commands:

# View service status
systemctl status [service_name]

# Enable at boot
systemctl enable [service_name]

# Start service immediately
systemctl start [service_name]

# View all enabled services
systemctl list-unit-files --type=service | grep enabled

For custom programs, create a .service file in /etc/systemd/system/.

Key Differences and Relationships

• Linux Service: A background daemon managed by init system (SysV init or systemd) with full lifecycle control (start, stop, restart, status).
• Boot Startup: An attribute of a service. A service can be set to start at boot, but not all auto-run commands are standard "services".
• Key Script Files:
  • /etc/rc.local: For user-defined commands.
  • /etc/inittab (legacy): Defines default runlevel and terminals.
  • /etc/profile & ~/.bash_profile: Shell environment scripts executed at user login - not for starting background services.

Summary and Best Practices

1. Prefer service management tools: For standard services, always use chkconfig (CentOS 6) or systemctl (CentOS 7+).
2. Use rc.local as supplement: For simple scripts/commands not easily packaged as services.
3. Check permissions: Ensure startup scripts and commands have proper execute permissions.
4. Specify runlevel: Server environments typically use runlevel 3 (no GUI), desktops use runlevel 5.
5. Version adaptation: CentOS/RHEL 7+ uses systemd - use corresponding systemctl commands.