diff --git a/sys/include/posix.h b/sys/include/posix.h
index c2b2a47..5de90cc 100644
--- a/sys/include/posix.h
+++ b/sys/include/posix.h
@@ -143,6 +143,7 @@ extern unsigned int POSIX_sleep(unsigned int seconds);
 extern int POSIX_pipe(int *errnop, int fildes[2]);
 extern int POSIX_umask(int *errnop, int mask);
 
+extern int POSIX_getpgrp(int *errnop);
 extern int POSIX_getuid(int *errnop);
 extern int POSIX_geteuid(int *errnop);
 extern int POSIX_setuid(int *errnop, int uid);
diff --git a/sys/src/lib/posix/ids.c b/sys/src/lib/posix/ids.c
index d130064..2a30d25 100644
--- a/sys/src/lib/posix/ids.c
+++ b/sys/src/lib/posix/ids.c
@@ -21,6 +21,61 @@
 #include <posix.h>
 #include "internal.h"
 
+int __libposix_session_leader = -1;
+
+static int
+get_noteid(int *errnop, int pid)
+{
+	int n, f;
+	char buf[30];
+
+	sprint(buf, "/proc/%d/noteid", pid);
+	f = open(buf, 0);
+	if(f < 0){
+		*errnop = __libposix_get_errno(PosixEPERM);
+		return -1;
+	}
+	n = read(f, buf, sizeof(buf) - 1);
+	if(n < 0){
+		*errnop = __libposix_get_errno(PosixEPERM);
+		return -1;
+	}
+	buf[n] = '\0';
+	n = atoi(buf);
+	close(f);
+
+	return n;
+}
+
+static int
+set_noteid(int *errnop, int pid, int noteid)
+{
+	int n, f;
+	char buf[30];
+
+	if(pid == 0)
+		pid = getpid();
+	if(noteid == 0){
+		noteid = get_noteid(errnop, pid);
+		if(noteid < 0)
+			return noteid;
+	}
+	sprint(buf, "/proc/%d/noteid", pid);
+	f = open(buf, 1);
+	if(f < 0) {
+		*errnop = __libposix_get_errno(PosixESRCH);
+		return -1;
+	}
+	n = sprint(buf, "%d", noteid);
+	n = write(f, buf, n);
+	if(n < 0){
+		*errnop = __libposix_get_errno(PosixEPERM);
+		return -1;
+	}
+	close(f);
+	return 0;
+}
+
 int
 POSIX_getuid(int *errnop)
 {
@@ -81,22 +136,58 @@ POSIX_setregid(int *errnop, int rgid, int egid)
 	return 0;
 }
 
+int
+POSIX_getpgrp(int *errnop)
+{
+	int pid = getpid();
+	return get_noteid(errnop, pid);
+}
+
 int
 POSIX_setpgid(int *errnop, int pid, int pgid)
 {
-	return 0;
+	if(pid < 0 || pgid < 0){
+		*errnop = __libposix_get_errno(PosixEINVAL);
+		return -1;
+	}
+	return set_noteid(errnop, pid, pgid);
 }
 
 int
 POSIX_getsid(int *errnop, int pid)
 {
-	return 0;
+	int reqnoteid, mynoteid;
+
+	if(pid < 0){
+		*errnop = __libposix_get_errno(PosixESRCH);
+		return -1;
+	}
+	if(pid == 0)
+		pid = getpid();
+	else if(pid == getpid())
+		return __libposix_session_leader;
+	reqnoteid = get_noteid(errnop, pid);
+	if(reqnoteid < 0)
+		return reqnoteid;
+	if(__libposix_session_leader < 0)
+		return reqnoteid;
+	mynoteid = POSIX_getpgrp(errnop);
+	if(mynoteid == reqnoteid){
+		/* if it share our pgrp (aka noteid), it shares
+		 * our session leader
+		 */
+		return __libposix_session_leader;
+	}
+	return reqnoteid;
 }
 
 int
 POSIX_setsid(int *errnop)
 {
-	*errnop = __libposix_get_errno(PosixEPERM);
-	return 0;
+	if(rfork(RFNAMEG|RFNOTEG) < 0){
+		*errnop = __libposix_get_errno(PosixEPERM);
+		return -1;
+	}
+	__libposix_session_leader = POSIX_getpgrp(errnop);
+	return __libposix_session_leader;
 }
-