Support writepid() calls by non-root programs to try using altpidpath() if rootpidpath() is not accessible

NEWS.adoc

@@ -41,6 +41,12 @@ https://github.com/networkupstools/nut/milestone/9
 
  - (expected) Bug fixes for fallout possible due to "fightwarn" effort in 2.8.0+
 
+ - common code:
+   * Revised common `writepid()` to use `altpidpath()` as location for the
+     PID file creation, if the default `rootpidpath()` is not accessible
+     (e.g. daemon was not initially started as `root`). Likewise updated
+     short PID file based signal sending to consult both locations. [#1717]
+
 
 PLANNED: Release notes for NUT 2.8.3 - what's new since 2.8.2
 -------------------------------------------------------------

common/common.c

@@ -1684,6 +1684,7 @@ void writepid(const char *name)
 	char	fn[SMALLBUF];
 	FILE	*pidf;
 	mode_t	mask;
+	intmax_t	initial_uid = getuid();
 
 	/* use full path if present, else build filename in PIDPATH */
 	if (*name == '/')
@@ -1693,6 +1694,10 @@ void writepid(const char *name)
 
 	mask = umask(022);
 	pidf = fopen(fn, "w");
+	if (!pidf && initial_uid) {
+		snprintf(fn, sizeof(fn), "%s/%s.pid", altpidpath(), name);
+		pidf = fopen(fn, "w");
+	}
 
 	if (pidf) {
 		intmax_t pid = (intmax_t)getpid();
@@ -2060,9 +2065,17 @@ int snprintfcat(char *dst, size_t size, const char *fmt, ...)
 #ifndef WIN32
 int sendsignal(const char *progname, int sig, int check_current_progname)
 {
-	char	fn[SMALLBUF];
+#ifdef UNIX_PATH_MAX
+	char	fn[UNIX_PATH_MAX];
+#else
+	char	fn[PATH_MAX];
+#endif
+	struct stat	st;
 
 	snprintf(fn, sizeof(fn), "%s/%s.pid", rootpidpath(), progname);
+	if (stat(fn, &st) != 0) {
+		snprintf(fn, sizeof(fn), "%s/%s.pid", altpidpath(), progname);
+	}
 
 	return sendsignalfn(fn, sig, progname, check_current_progname);
 }

common/nutipc.cpp

@@ -44,6 +44,7 @@
 #include "nutstream.hpp"
 
 #include <iostream>
+#include <sys/stat.h>
 
 
 namespace nut {
@@ -297,14 +298,21 @@ int Signal::send(Signal::enum_t signame, const std::string & pid_file) {
 
 int NutSignal::send(NutSignal::enum_t signame, const std::string & process) {
 	std::string pid_file;
+	struct stat	st;
 
-	// FIXME: What about ALTPIDPATH (for non-root daemons)
-	// and shouldn't we also consider it (e.g. try/catch)?
 	pid_file += rootpidpath();
 	pid_file += '/';
 	pid_file += process;
 	pid_file += ".pid";
 
+	if (::stat(pid_file.c_str(), &st) != 0) {
+		// Consider ALTPIDPATH (used by non-root daemons)
+		pid_file  = altpidpath();
+		pid_file += '/';
+		pid_file += process;
+		pid_file += ".pid";
+	}
+
 	return Signal::send(signame, pid_file);
 }
 

docs/nut.dict

@@ -1,4 +1,4 @@
-personal_ws-1.1 en 3270 utf-8
+personal_ws-1.1 en 3273 utf-8
 AAC
 AAS
 ABI
@@ -2740,6 +2740,7 @@ roadmap
 rootca
 rootfs
 rootfs'es
+rootpidpath
 rq
 rqt
 rsa
@@ -3215,6 +3216,7 @@ workspaceFolder
 workspaces
 writability
 writeinfo
+writepid
 writeups
 ws
 xAAAA