NimD now checks if another instance is running before starting up

README.md

@@ -121,4 +121,5 @@ sigtermDelay         = 90                    # Delay (seconds) that nimd will wa
 ## Testing NimD
 
 NimD is not quite ready for production yet, but in the `scripts` folder you can find a few simple bash scripts to test NimD
-in a minimal Alpine Linux VM using QEMU.
+in a minimal Alpine Linux VM using QEMU. Note that due to weirdness in how stdout is handled on the VGA port, the VM will use
+the serial port (ttyS0) as output by default (you can change this in the kernel parameters)

scripts/rebuild.sh

@@ -1,7 +1,10 @@
-nim -o:rootfs/bin/nimd -d:release --gc:orc --opt:size --passL:"-static" compile src/main.nim
+# Build the environment
-nim -o:rootfs/bin/nimdown -d:release --gc:orc --opt:size --passL:"-static" compile src/programs/poweroff.nim
-nim -o:rootfs/bin/nimhalt -d:release --gc:orc --opt:size --passL:"-static" compile src/programs/halt.nim
-nim -o:rootfs/bin/nimreboot -d:release --gc:orc --opt:size --passL:"-static" compile src/programs/reboot.nim
 mkdir -p rootfs/etc/nimd
 cp nimd.conf rootfs/etc/nimd/nimd.conf
-./boot.sh --kernel vmlinuz-linux --initrd initrd-linux.img --memory 1G --build
+nim -o:rootfs/bin/nimd      -d:release --gc:orc --opt:size --passL:"-static" compile src/main.nim
+nim -o:rootfs/bin/halt      -d:release --gc:orc --opt:size --passL:"-static" compile src/programs/halt.nim
+nim -o:rootfs/bin/reboot    -d:release --gc:orc --opt:size --passL:"-static" compile src/programs/reboot.nim
+nim -o:rootfs/bin/poweroff  -d:release --gc:orc --opt:size --passL:"-static" compile src/programs/poweroff.nim
+
+# Start the VM
+./scripts/boot.sh --kernel vmlinuz-linux --initrd initrd-linux.img --memory 1G --build

scripts/start.sh

@@ -1 +1 @@
-./boot.sh --kernel vmlinuz-linux --initrd initrd-linux.img --memory 1G
+./scripts/boot.sh --kernel vmlinuz-linux --initrd initrd-linux.img --memory 1G

src/core/mainloop.nim

@@ -28,8 +28,8 @@ proc mainLoop*(logger: Logger, config: NimDConfig, startServices: bool = true) =
     if startServices:
         logger.info("Processing default runlevel")
         startServices(logger, workers=config.workers, level=Default)
-        logger.debug(&"Unblocking signals")
+    logger.debug(&"Unblocking signals")
-        unblockSignals(logger)
+    unblockSignals(logger)
     logger.info("System initialization complete, idling on control socket")
     var opType: string
     try:
@@ -52,6 +52,7 @@ proc mainLoop*(logger: Logger, config: NimDConfig, startServices: bool = true) =
             # - 'h' -> halt
             # - 's' -> Services-related operations (start, stop, get status, etc.)
             # - 'l' -> Reload in-memory configuration
+            # - 'c' -> Check NimD status (returns "1" if up)
             case opType:
                 of "p":
                     logger.info("Received shutdown request")
@@ -63,11 +64,14 @@ proc mainLoop*(logger: Logger, config: NimDConfig, startServices: bool = true) =
                     logger.info("Received halt request")
                     halt(logger)
                 of "s":
-                    logger.info("Received service request")
+                    logger.info("Received service-related request")
                     # TODO: Operate on services
                 of "l":
                     logger.info("Received reload request")
                     mainLoop(logger, parseConfig(logger, "/etc/nimd/nimd.conf"), startServices=false)
+                of "c":
+                    logger.info("Received check request, responding")
+                    clientSocket.send("1")
                 else:
                     logger.warning(&"Received unknown operation type '{opType}' via control socket, ignoring it")
                     discard

src/core/shutdown.nim

@@ -119,7 +119,6 @@ proc nimDExit*(logger: Logger, code: int, emerg: bool = true) =
         logger.info("Terminating child processes with SIGKILL")
         discard posix.kill(-1, SIGKILL)
     logger.warning("Shutdown procedure complete, NimD is exiting")
-    quit(-1)
 
 
 proc reboot*(logger: Logger) =

src/main.nim

@@ -14,6 +14,7 @@
 import parseopt
 import strformat
 import posix
+import net
 import os
 
 # NimD's own stuff
@@ -68,10 +69,51 @@ proc addStuff =
     addService(shell)
 
 
+proc checkControlSocket(logger: Logger, config: NimDConfig): bool =
+    ## Performs some startup checks on nim's control
+    ## socket
+    result = true
+    var stat_result: Stat
+    if posix.stat(cstring(config.sock), stat_result) == -1:
+        logger.warning(&"Could not stat() {config.sock}, assuming NimD instance isn't running")
+    # I stole this from /usr/lib/python3.10/stat.py
+    elif (int(stat_result.st_mode) and 0o170000) != 0o140000:
+        logger.fatal(&"{config.sock} exists and is not a socket")
+        result = false
+    elif dirExists(config.sock):
+        logger.info("Control socket path is a directory, appending nimd.sock to it")
+        config.sock = config.sock.joinPath("nimd.sock")
+    else:
+        logger.debug("Trying to reach current NimD instance")
+        var sock = newSocket(Domain.AF_UNIX, SockType.SOCK_STREAM, Protocol.IPPROTO_IP)
+        try:
+            sock.connectUnix(config.sock)
+            logger.info("Control socket already exists, trying to reach current NimD instance")
+        except OSError:
+            logger.warning(&"Could not connect to control socket at {config.sock} ({getCurrentExceptionMsg()}), assuming NimD instance isn't running")
+            try:
+                removeFile(config.sock)
+            except OSError:
+                logger.warning(&"Could not delete dangling control socket at {config.sock} ({getCurrentExceptionMsg()})")
+        if sock.trySend("c"):
+            try:
+                if sock.recv(1, timeout=5) == "1":
+                    logger.error("Another NimD instance is running! Exiting")
+                    result = false
+            except OSError:
+                logger.warning(&"Could not read from control socket at {config.sock} ({getCurrentExceptionMsg()}), assuming NimD instance isn't running")
+            except TimeoutError:
+                logger.warning(&"Could not read from control socket at {config.sock} ({getCurrentExceptionMsg()}), assuming NimD instance isn't running")
+        else:
+            logger.fatal(&"Could not write on control socket at {config.sock}")
+            result = false
+
 
 proc main(logger: Logger, config: NimDConfig) =
     ## NimD's entry point and setup
     ## function
+    if not checkControlSocket(logger, config):
+        return
     logger.debug(&"Setting log file to '{config.logFile}'")
     setLogFile(file=config.logFile)
     logger.debug("Starting NimD: A minimal, self-contained, dependency-based Linux init system written in Nim")
@@ -173,8 +215,7 @@ when isMainModule:
                         quit(EINVAL) # EINVAL - Invalid argument
             else:
                 echo "Usage: nimd [options]"
-                quit(EINVAL) # EINVAL - Invalid argument
+                quit(EINVAL) # EINVAL - Invalid argument        
-
     setStdIoUnbuffered()   # Colors don't work otherwise!
     try:
         main(logger, parseConfig(logger, "/etc/nimd/nimd.conf"))