diff --git a/Sources/Basics/Concurrency/PID.swift b/Sources/Basics/Concurrency/PID.swift
new file mode 100644
index 00000000000..fe9593b91e4
--- /dev/null
+++ b/Sources/Basics/Concurrency/PID.swift
@@ -0,0 +1,76 @@
+//
+//  PID.swift
+//  SwiftPM
+//
+//  Created by John Bute on 2025-04-24.
+//
+
+import Foundation
+
+public protocol pidFileManipulator {
+    var scratchDirectory: AbsolutePath {get set}
+
+    init(scratchDirectory: AbsolutePath)
+    
+    func readPID() -> Int32?
+    func deletePIDFile() throws
+    func writePID(pid: pid_t) throws
+    func getCurrentPID() -> Int32
+}
+
+
+
+public struct pidFile: pidFileManipulator {
+    
+    public var scratchDirectory: AbsolutePath
+    
+    public init(scratchDirectory: AbsolutePath) {
+        self.scratchDirectory = scratchDirectory
+    }
+    
+    /// Return the path of the PackageManager.lock.pid file where the PID is located
+    private var pidFilePath: AbsolutePath {
+        return self.scratchDirectory.appending(component: "PackageManager.lock.pid")
+    }
+
+    /// Read the pid file
+    public func readPID() -> Int32? {
+        // Check if the file exists
+        let filePath = pidFilePath.pathString
+        guard FileManager.default.fileExists(atPath: filePath)  else {
+            print("File does not exist at path: \(filePath)")
+            return nil
+        }
+
+        do {
+            // Read the contents of the file
+            let pidString = try String(contentsOf: pidFilePath.asURL, encoding: .utf8).trimmingCharacters(in: .whitespacesAndNewlines)
+
+            // Check if the PID string can be converted to an Int32
+            if let pid = Int32(pidString) {
+                return pid
+            } else {
+                return nil
+            }
+        } catch {
+            // Catch any errors and print them
+            return nil
+        }
+    }
+
+    /// Get the current PID of the process
+    public func getCurrentPID() -> Int32 {
+        return getpid()
+    }
+
+    /// Write .pid file containing PID of process currently using .build directory
+    public func writePID(pid: pid_t) throws {
+        try "\(pid)".write(to: pidFilePath.asURL, atomically: true, encoding: .utf8)
+    }
+    
+    /// Delete PID file at URL
+    public func deletePIDFile() throws {
+        try FileManager.default.removeItem(at: pidFilePath.asURL)
+    }
+
+}
diff --git a/Sources/CoreCommands/SwiftCommandState.swift b/Sources/CoreCommands/SwiftCommandState.swift
index 12e193d838f..8428e4a0c93 100644
--- a/Sources/CoreCommands/SwiftCommandState.swift
+++ b/Sources/CoreCommands/SwiftCommandState.swift
@@ -14,7 +14,7 @@ import _Concurrency
 import ArgumentParser
 import Basics
 import Dispatch
-import class Foundation.NSLock
+import class Foundation.NSDistributedLock
 import class Foundation.ProcessInfo
 import PackageGraph
 import PackageLoading
@@ -22,6 +22,7 @@ import PackageLoading
 import PackageModel
 import SPMBuildCore
 import Workspace
+import Foundation.NSFileManager
 
 #if USE_IMPL_ONLY_IMPORTS
 @_implementationOnly
@@ -287,6 +288,7 @@ public final class SwiftCommandState {
 
     private let hostTriple: Basics.Triple?
 
+    private let pidManipulator: pidFileManipulator
     package var preferredBuildConfiguration = BuildConfiguration.debug
 
     /// Create an instance of this tool.
@@ -324,7 +326,8 @@ public final class SwiftCommandState {
         createPackagePath: Bool,
         hostTriple: Basics.Triple? = nil,
         fileSystem: any FileSystem = localFileSystem,
-        environment: Environment = .current
+        environment: Environment = .current,
+        pidManipulator: pidFileManipulator? = nil
     ) throws {
         self.hostTriple = hostTriple
         self.fileSystem = fileSystem
@@ -407,6 +410,8 @@ public final class SwiftCommandState {
         self.sharedSwiftSDKsDirectory = try fileSystem.getSharedSwiftSDKsDirectory(
             explicitDirectory: options.locations.swiftSDKsDirectory ?? options.locations.deprecatedSwiftSDKsDirectory
         )
+        
+        self.pidManipulator = pidManipulator ?? pidFile(scratchDirectory: self.scratchDirectory)
 
         // set global process logging handler
         AsyncProcess.loggingHandler = { self.observabilityScope.emit(debug: $0) }
@@ -1056,33 +1061,43 @@ public final class SwiftCommandState {
 
         let workspaceLock = try FileLock.prepareLock(fileToLock: self.scratchDirectory)
 
+        var lockAcquired = false
+
         // Try a non-blocking lock first so that we can inform the user about an already running SwiftPM.
         do {
             try workspaceLock.lock(type: .exclusive, blocking: false)
+            lockAcquired = true
         } catch ProcessLockError.unableToAquireLock(let errno) {
             if errno == EWOULDBLOCK {
+                let existingPID = self.pidManipulator.readPID()
+                let pidInfo = existingPID.map { "(PID: \($0)) " } ?? ""
                 if self.options.locations.ignoreLock {
                     self.outputStream
                         .write(
-                            "Another instance of SwiftPM is already running using '\(self.scratchDirectory)', but this will be ignored since `--ignore-lock` has been passed"
+                            "Another instance of SwiftPM (pid \(pidInfo) is already running using '\(self.scratchDirectory)', but this will be ignored since `--ignore-lock` has been passed"
                                 .utf8
                         )
                     self.outputStream.flush()
                 } else {
                     self.outputStream
                         .write(
-                            "Another instance of SwiftPM is already running using '\(self.scratchDirectory)', waiting until that process has finished execution..."
+                            "Another instance of SwiftPM (pid \(pidInfo) is already running using '\(self.scratchDirectory)', waiting until that process has finished execution..."
                                 .utf8
                         )
                     self.outputStream.flush()
 
                     // Only if we fail because there's an existing lock we need to acquire again as blocking.
                     try workspaceLock.lock(type: .exclusive, blocking: true)
+                    lockAcquired = true
                 }
             }
         }
 
         self.workspaceLock = workspaceLock
+        
+        if lockAcquired || self.options.locations.ignoreLock {
+            try self.pidManipulator.writePID(pid: self.pidManipulator.getCurrentPID())
+        }
     }
 
     fileprivate func releaseLockIfNeeded() {
@@ -1094,6 +1109,12 @@ public final class SwiftCommandState {
         self.workspaceLockState = .unlocked
 
         self.workspaceLock?.unlock()
+        
+        do {
+            try self.pidManipulator.deletePIDFile()
+        } catch {
+            self.observabilityScope.emit(warning: "Failed to delete PID file: \(error)")
+        }
     }
 }