procd — Process Manager

procd: OpenWrt’s init system, service supervisor, and hotplug handler.

procd is OpenWrt’s PID 1 init system. It handles early boot, service supervision, hotplug events, and integrates with ubus to expose a service management API.

Components

Component	Description
init	Runs as PID 1 during early boot, sets up the system
procd	Service supervisor: starts, monitors, and restarts services
udevtrigger	Replays udev events on boot to trigger hotplug
upgraded	Handles sysupgrade coordination
askfirst	Spawns a getty/shell on the console at first boot

Additional optional packages:

Package	Description
procd-ujail	Process jail helper using Linux namespaces
procd-seccomp	Seccomp syscall filter support
uxc	Container management using procd-ujail

Service Script Structure

All init scripts live in /etc/init.d/ and use the /etc/rc.common framework:

#!/bin/sh /etc/rc.common

USE_PROCD=1
START=95
STOP=05

start_service() {
    procd_open_instance
    procd_set_param command /usr/sbin/my-daemon --foreground
    procd_set_param env MY_VAR=value
    procd_set_param respawn ${respawn_threshold:-3600} ${respawn_timeout:-5} ${respawn_retry:-5}
    procd_set_param limits core="unlimited"
    procd_set_param file /etc/config/my-service
    procd_set_param stdout 1
    procd_set_param stderr 1
    procd_close_instance
}

procd_set_param Parameters

Parameter	Description
command	The command and arguments to execute
env	Environment variable(s) to set
respawn [threshold] [timeout] [retry]	Auto-restart settings. threshold: crash-free seconds before reset. timeout: seconds between restarts. retry: max restarts before giving up (0 = infinite).
limits	Process resource limits (core, nofile, nproc, etc.)
file	Config file(s) to watch; service restarts when these change
netdev	Network interface to watch
stdout	Redirect stdout to syslog (1=enable)
stderr	Redirect stderr to syslog (1=enable)
pidfile	Path to write the service PID
user	Run the service as this user
group	Run the service as this group

START and STOP Values

START and STOP are integer ordering values (0–99). Services with lower START values start earlier. STOP is used for shutdown ordering.

Init Script Commands

# Enable a service (creates symlink in /etc/rc.d/)
/etc/init.d/my-service enable

# Disable a service
/etc/init.d/my-service disable

# Start / stop / restart
/etc/init.d/my-service start
/etc/init.d/my-service stop
/etc/init.d/my-service restart

# Reload configuration without restarting
/etc/init.d/my-service reload

# Show status
/etc/init.d/my-service status

Enabling a service creates a symlink:

/etc/rc.d/S95my-service -> /etc/init.d/my-service

procd via ubus

procd exposes a service object on ubus for runtime service management:

# List all services and their instances
ubus call service list

# Get details for a specific service
ubus call service list '{"name":"dnsmasq"}'

# Start a service instance programmatically
ubus call service set '{
  "name": "my-app",
  "instances": {
    "instance1": {
      "command": ["/usr/bin/my-app", "--arg1"]
    }
  }
}'

# Delete a service
ubus call service delete '{"name":"my-app"}'

# Send a signal to a service
ubus call service signal '{"name":"my-app","signal":15}'

Hotplug Subsystem

procd handles hotplug events (USB insertion, network link changes, etc.) by executing scripts from:

/etc/hotplug.d/<subsystem>/

The <subsystem> matches the kernel’s hotplug subsystem name:

Subsystem	Triggered by
block	Block devices (USB storage, SD cards)
net	Network interface changes
usb	USB device insertion/removal
button	GPIO button events
ieee80211	Wi-Fi radio events

Example hotplug script:

#!/bin/sh
# /etc/hotplug.d/block/10-mount

[ "$ACTION" = "add" ] || exit 0
[ -b "/dev/$DEVNAME" ] || exit 0

mkdir -p /mnt/$DEVNAME
mount /dev/$DEVNAME /mnt/$DEVNAME

Available Hotplug Variables

Variable	Description
$ACTION	add, remove, change, bind, unbind
$DEVNAME	Device name (e.g., sda1, eth1)
$SUBSYSTEM	Kernel subsystem
$DEVTYPE	Device type (e.g., disk, partition)

Minimal Service Example

#!/bin/sh /etc/rc.common
# /etc/init.d/hello

USE_PROCD=1
START=99
STOP=01

start_service() {
    procd_open_instance
    procd_set_param command /bin/sh -c 'while true; do echo hello; sleep 60; done'
    procd_set_param respawn
    procd_close_instance
}

After placing this file at /etc/init.d/hello:

chmod +x /etc/init.d/hello
/etc/init.d/hello enable
/etc/init.d/hello start