Do not use PWD unless it actually matches the real working directory.

client.c

@@ -222,7 +222,7 @@ client_main(struct event_base *base, int argc, char **argv, int flags)
 	const char		*ttynam, *cwd;
 	pid_t			 ppid;
 	enum msgtype		 msg;
-	char			*cause, path[PATH_MAX];
+	char			*cause;
 	struct termios		 tio, saved_tio;
 	size_t			 size;
 
@@ -277,9 +277,7 @@ client_main(struct event_base *base, int argc, char **argv, int flags)
 	client_peer = proc_add_peer(client_proc, fd, client_dispatch, NULL);
 
 	/* Save these before pledge(). */
-	if ((cwd = getenv("PWD")) == NULL &&
-	    (cwd = getcwd(path, sizeof path)) == NULL &&
-	    (cwd = find_home()) == NULL)
+	if ((cwd = find_cwd()) == NULL && (cwd = find_home()) == NULL)
 		cwd = "/";
 	if ((ttynam = ttyname(STDIN_FILENO)) == NULL)
 		ttynam = "";

tmux.c

@@ -166,6 +166,31 @@ setblocking(int fd, int state)
 	}
 }
 
+const char *
+find_cwd(void)
+{
+	char		 resolved1[PATH_MAX], resolved2[PATH_MAX];
+	static char	 cwd[PATH_MAX];
+	const char	*pwd;
+
+	if (getcwd(cwd, sizeof cwd) == NULL)
+		return (NULL);
+	if ((pwd = getenv("PWD")) == NULL || *pwd == '\0')
+		return (cwd);
+
+	/*
+	 * We want to use PWD so that symbolic links are maintained,
+	 * but only if it matches the actual working directory.
+	 */
+	if (realpath(pwd, resolved1) == NULL)
+		return (cwd);
+	if (realpath(cwd, resolved2) == NULL)
+		return (cwd);
+	if (strcmp(resolved1, resolved2) != 0)
+		return (cwd);
+	return (pwd);
+}
+
 const char *
 find_home(void)
 {
@@ -191,7 +216,6 @@ int
 main(int argc, char **argv)
 {
 	char					*path, *label, *cause, **var;
-	char					 tmp[PATH_MAX];
 	const char				*s, *shell, *cwd;
 	int					 opt, flags, keys;
 	const struct options_table_entry	*oe;
@@ -293,8 +317,7 @@ main(int argc, char **argv)
 	global_environ = environ_create();
 	for (var = environ; *var != NULL; var++)
 		environ_put(global_environ, *var);
-	if ((cwd = getenv("PWD")) == NULL &&
-	    (cwd = getcwd(tmp, sizeof tmp)) != NULL)
+	if ((cwd = find_cwd()) != NULL)
 		environ_set(global_environ, "PWD", "%s", cwd);
 
 	global_options = options_create(NULL);

tmux.h

@@ -1506,6 +1506,7 @@ extern int		 ptm_fd;
 extern const char	*shell_command;
 int		 areshell(const char *);
 void		 setblocking(int, int);
+const char	*find_cwd(void);
 const char	*find_home(void);
 
 /* proc.c */