diff --git a/sys/man/2/dup b/sys/man/2/dup
index cd3414106..1eca0a713 100644
--- a/sys/man/2/dup
+++ b/sys/man/2/dup
@@ -32,6 +32,19 @@ requires that
 .I newfd
 be no greater than 20 more than the highest file descriptor ever used by
 the program.
+.PP
+.I Dup
+does not copy the per file descriptor
+.B OCEXEC
+flag,
+meaning that
+.I newfd
+will not be closed on
+.IR exec(2)
+syscall,
+when
+.I oldfd
+had been previously opend with it.
 .SH SOURCE
 .B /sys/src/libc/9syscall
 .SH SEE ALSO
diff --git a/sys/src/9/port/auth.c b/sys/src/9/port/auth.c
index 2cc54c657..b6b19bd63 100644
--- a/sys/src/9/port/auth.c
+++ b/sys/src/9/port/auth.c
@@ -97,13 +97,12 @@ sysfauth(va_list list)
 		nexterror();
 	}
 
-	fd = newfd(ac);
+	/* always mark it close on exec */
+	fd = newfd(ac, OCEXEC);
 	if(fd < 0)
 		error(Enofd);
 	poperror();	/* ac */
 
-	/* always mark it close on exec */
-	ac->flag |= CCEXEC;
 	return (uintptr)fd;
 }
 
diff --git a/sys/src/9/port/chan.c b/sys/src/9/port/chan.c
index 58a47cc83..e60561d1a 100644
--- a/sys/src/9/port/chan.c
+++ b/sys/src/9/port/chan.c
@@ -1468,9 +1468,6 @@ namec(char *aname, int amode, int omode, ulong perm)
 			saveregisters();
 
 			c = devtab[c->type]->open(c, omode&~OCEXEC);
-
-			if(omode & OCEXEC)
-				c->flag |= CCEXEC;
 			if(omode & ORCLOSE)
 				c->flag |= CRCLOSE;
 			break;
@@ -1571,11 +1568,9 @@ namec(char *aname, int amode, int omode, ulong perm)
 			incref(cnew->path);
 
 			cnew = devtab[cnew->type]->create(cnew, e.elems[e.nelems-1], omode&~(OEXCL|OCEXEC), perm);
-			poperror();
-			if(omode & OCEXEC)
-				cnew->flag |= CCEXEC;
 			if(omode & ORCLOSE)
 				cnew->flag |= CRCLOSE;
+			poperror();
 			putmhead(m);
 			cclose(c);
 			c = cnew;
diff --git a/sys/src/9/port/devdup.c b/sys/src/9/port/devdup.c
index 2ba718729..79c7d90ff 100644
--- a/sys/src/9/port/devdup.c
+++ b/sys/src/9/port/devdup.c
@@ -63,6 +63,8 @@ dupopen(Chan *c, int omode)
 	Chan *f;
 	int fd, twicefd;
 
+	if(omode & ORCLOSE)
+		error(Eperm);
 	if(c->qid.type & QTDIR){
 		if(omode != 0)
 			error(Eisdir);
diff --git a/sys/src/9/port/devshr.c b/sys/src/9/port/devshr.c
index 96e319221..225ba6c93 100644
--- a/sys/src/9/port/devshr.c
+++ b/sys/src/9/port/devshr.c
@@ -396,6 +396,8 @@ shropen(Chan *c, int omode)
 	case Qcmpt:
 		if(omode&OTRUNC)
 			error(Eexist);
+		if(omode&ORCLOSE)
+			error(Eperm);
 		shr = sch->shr;
 		mpt = sch->mpt;
 		devpermcheck(mpt->owner, mpt->perm, mode);
diff --git a/sys/src/9/port/devsrv.c b/sys/src/9/port/devsrv.c
index 193fa6c8b..8128569a1 100644
--- a/sys/src/9/port/devsrv.c
+++ b/sys/src/9/port/devsrv.c
@@ -135,6 +135,8 @@ srvopen(Chan *c, int omode)
 
 	if(omode&OTRUNC)
 		error(Eexist);
+	if(omode&ORCLOSE)
+		error(Eperm);
 	if(openmode(omode)!=sp->chan->mode && sp->chan->mode!=ORDWR)
 		error(Eperm);
 	devpermcheck(sp->owner, sp->perm, omode);
@@ -338,8 +340,6 @@ srvwrite(Chan *c, void *va, long n, vlong)
 		cclose(c1);
 		nexterror();
 	}
-	if(c1->flag & (CCEXEC|CRCLOSE))
-		error("posted fd has remove-on-close or close-on-exec");
 	if(c1->qid.type & QTAUTH)
 		error("cannot post auth file in srv");
 	sp = srvlookup(nil, c->qid.path);
diff --git a/sys/src/9/port/lib.h b/sys/src/9/port/lib.h
index 1f7bf7d1d..06b423d9d 100644
--- a/sys/src/9/port/lib.h
+++ b/sys/src/9/port/lib.h
@@ -176,7 +176,7 @@ extern	void	qsort(void*, long, long, int (*)(void*, void*));
 #define	ORDWR	2	/* read and write */
 #define	OEXEC	3	/* execute, == read but check execute permission */
 #define	OTRUNC	16	/* or'ed in (except for exec), truncate file first */
-#define	OCEXEC	32	/* or'ed in, close on exec */
+#define	OCEXEC	32	/* or'ed in (per file descriptor), close on exec */
 #define	ORCLOSE	64	/* or'ed in, remove on close */
 #define OEXCL   0x1000	/* or'ed in, exclusive create */
 
diff --git a/sys/src/9/port/pgrp.c b/sys/src/9/port/pgrp.c
index 5576acc57..408370d35 100644
--- a/sys/src/9/port/pgrp.c
+++ b/sys/src/9/port/pgrp.c
@@ -140,7 +140,8 @@ dupfgrp(Fgrp *f)
 
 	new = smalloc(sizeof(Fgrp));
 	if(f == nil){
-		new->fd = smalloc(DELTAFD*sizeof(Chan*));
+		new->flag = smalloc(DELTAFD*sizeof(new->flag[0]));
+		new->fd = smalloc(DELTAFD*sizeof(new->fd[0]));
 		new->nfd = DELTAFD;
 		new->ref = 1;
 		return new;
@@ -152,12 +153,19 @@ dupfgrp(Fgrp *f)
 	i = new->nfd%DELTAFD;
 	if(i != 0)
 		new->nfd += DELTAFD - i;
-	new->fd = malloc(new->nfd*sizeof(Chan*));
+	new->fd = malloc(new->nfd*sizeof(new->fd[0]));
 	if(new->fd == nil){
 		unlock(f);
 		free(new);
 		error("no memory for fgrp");
 	}
+	new->flag = malloc(new->nfd*sizeof(new->flag[0]));
+	if(new->flag == nil){
+		unlock(f);
+		free(new->fd);
+		free(new);
+		error("no memory for fgrp");
+	}
 	new->ref = 1;
 
 	new->maxfd = f->maxfd;
@@ -165,6 +173,7 @@ dupfgrp(Fgrp *f)
 		if((c = f->fd[i]) != nil){
 			incref(c);
 			new->fd[i] = c;
+			new->flag[i] = f->flag[i];
 		}
 	}
 	unlock(f);
@@ -194,6 +203,7 @@ closefgrp(Fgrp *f)
 	up->closingfgrp = nil;
 
 	free(f->fd);
+	free(f->flag);
 	free(f);
 }
 
diff --git a/sys/src/9/port/portdat.h b/sys/src/9/port/portdat.h
index 7c9aa7193..a5cdafa6a 100644
--- a/sys/src/9/port/portdat.h
+++ b/sys/src/9/port/portdat.h
@@ -125,7 +125,7 @@ enum
 	COPEN	= 0x0001,		/* for i/o */
 	CMSG	= 0x0002,		/* the message channel for a mount */
 /*rsc	CCREATE	= 0x0004,		/* permits creation if c->mnt */
-	CCEXEC	= 0x0008,		/* close on exec */
+	CCEXEC	= 0x0008,		/* close on exec (per file descriptor) */
 	CFREE	= 0x0010,		/* not in use */
 	CRCLOSE	= 0x0020,		/* remove on close */
 	CCACHE	= 0x0080,		/* client cache */
@@ -509,6 +509,7 @@ struct Fgrp
 	Ref;
 	Lock;
 	Chan	**fd;
+	uchar	*flag;			/* per file-descriptor flags (CCEXEC) */
 	int	nfd;			/* number allocated */
 	int	maxfd;			/* highest fd in use */
 	int	exceed;			/* debugging */
diff --git a/sys/src/9/port/portfns.h b/sys/src/9/port/portfns.h
index 04550987f..00c7e8b96 100644
--- a/sys/src/9/port/portfns.h
+++ b/sys/src/9/port/portfns.h
@@ -201,7 +201,7 @@ Chan*		namec(char*, int, int, ulong);
 void		nameerror(char*, char*);
 int		needpages(void*);
 Chan*		newchan(void);
-int		newfd(Chan*);
+int		newfd(Chan*, int);
 Mhead*		newmhead(Chan*);
 Mount*		newmount(Chan*, int, char*);
 Page*		newpage(int, Segment **, uintptr);
diff --git a/sys/src/9/port/sysfile.c b/sys/src/9/port/sysfile.c
index ed8e5c7ad..a503b2cca 100644
--- a/sys/src/9/port/sysfile.c
+++ b/sys/src/9/port/sysfile.c
@@ -25,33 +25,45 @@ int
 growfd(Fgrp *f, int fd)	/* fd is always >= 0 */
 {
 	Chan **newfd, **oldfd;
+	uchar *newflag, *oldflag;
+	int nfd;
 
-	if(fd < f->nfd)
+	nfd = f->nfd;
+	if(fd < nfd)
 		return 0;
-	if(fd >= f->nfd+DELTAFD)
+	if(fd >= nfd+DELTAFD)
 		return -1;	/* out of range */
 	/*
 	 * Unbounded allocation is unwise; besides, there are only 16 bits
 	 * of fid in 9P
 	 */
-	if(f->nfd >= 5000){
+	if(nfd >= 5000){
     Exhausted:
 		print("no free file descriptors\n");
 		return -1;
 	}
-	newfd = malloc((f->nfd+DELTAFD)*sizeof(Chan*));
+	oldfd = f->fd;
+	oldflag = f->flag;
+	newfd = malloc((nfd+DELTAFD)*sizeof(newfd[0]));
 	if(newfd == nil)
 		goto Exhausted;
-	oldfd = f->fd;
-	memmove(newfd, oldfd, f->nfd*sizeof(Chan*));
+	memmove(newfd, oldfd, nfd*sizeof(newfd[0]));
+	newflag = malloc((nfd+DELTAFD)*sizeof(newflag[0]));
+	if(newflag == nil){
+		free(newfd);
+		goto Exhausted;
+	}
+	memmove(newflag, oldflag, nfd*sizeof(newflag[0]));
 	f->fd = newfd;
-	free(oldfd);
-	f->nfd += DELTAFD;
+	f->flag = newflag;
+	f->nfd = nfd+DELTAFD;
 	if(fd > f->maxfd){
 		if(fd/100 > f->maxfd/100)
 			f->exceed = (fd/100)*100;
 		f->maxfd = fd;
 	}
+	free(oldfd);
+	free(oldflag);
 	return 1;
 }
 
@@ -72,9 +84,9 @@ findfreefd(Fgrp *f, int start)
 }
 
 int
-newfd(Chan *c)
+newfd(Chan *c, int mode)
 {
-	int fd;
+	int fd, flag;
 	Fgrp *f;
 
 	f = up->fgrp;
@@ -87,6 +99,13 @@ newfd(Chan *c)
 	if(fd > f->maxfd)
 		f->maxfd = fd;
 	f->fd[fd] = c;
+
+	/* per file-descriptor flags */
+	flag = 0;
+	if(mode & OCEXEC)
+		flag |= CCEXEC;
+	f->flag[fd] = flag;
+
 	unlockfgrp(f);
 	return fd;
 }
@@ -112,6 +131,8 @@ newfd2(int fd[2], Chan *c[2])
 		f->maxfd = fd[1];
 	f->fd[fd[0]] = c[0];
 	f->fd[fd[1]] = c[1];
+	f->flag[fd[0]] = 0;
+	f->flag[fd[1]] = 0;
 	unlockfgrp(f);
 	return 0;
 }
@@ -247,6 +268,7 @@ sysdup(va_list list)
 
 		oc = f->fd[fd];
 		f->fd[fd] = c;
+		f->flag[fd] = 0;
 		unlockfgrp(f);
 		if(oc != nil)
 			cclose(oc);
@@ -255,7 +277,7 @@ sysdup(va_list list)
 			cclose(c);
 			nexterror();
 		}
-		fd = newfd(c);
+		fd = newfd(c, 0);
 		if(fd < 0)
 			error(Enofd);
 		poperror();
@@ -280,7 +302,7 @@ sysopen(va_list list)
 		cclose(c);
 		nexterror();
 	}
-	fd = newfd(c);
+	fd = newfd(c, mode);
 	if(fd < 0)
 		error(Enofd);
 	poperror();
@@ -295,7 +317,7 @@ fdclose(int fd, int flag)
 
 	lock(f);
 	c = fd <= f->maxfd ? f->fd[fd] : nil;
-	if(c == nil || (flag != 0 && (c->flag&flag) == 0)){
+	if(c == nil || (flag != 0 && ((f->flag[fd]|c->flag)&flag) == 0)){
 		unlock(f);
 		return;
 	}
@@ -1166,7 +1188,7 @@ syscreate(va_list list)
 		cclose(c);
 		nexterror();
 	}
-	fd = newfd(c);
+	fd = newfd(c, mode);
 	if(fd < 0)
 		error(Enofd);
 	poperror();