diff --git a/kernel-src/include/kernel/abi.h b/kernel-src/include/kernel/abi.h
index 4733b7bb..293e39fd 100644
--- a/kernel-src/include/kernel/abi.h
+++ b/kernel-src/include/kernel/abi.h
@@ -94,6 +94,7 @@ typedef struct {
 #define MSG_CMSG_CLOEXEC 0x40000000
 #define MSG_CTRUNC 0x8
 #define MSG_PEEK 2
+#define MSG_DONTWAIT 0x40
 #define MSG_WAITALL 0x100
 #define MSG_NOSIGNAL 0x4000
 
diff --git a/kernel-src/sys/syscalls/accept.c b/kernel-src/sys/syscalls/accept.c
index a585d5e7..d7c64c8e 100644
--- a/kernel-src/sys/syscalls/accept.c
+++ b/kernel-src/sys/syscalls/accept.c
@@ -28,6 +28,11 @@ syscallret_t syscall_accept(context_t *, int oldfd, abisockaddr_t *abisockaddr,
 
 	socket_t *server = SOCKFS_SOCKET_FROM_NODE(oldfile->vnode);
 
+	if (server->ops->accept == NULL) {
+		ret.errno = ENOTSUP;
+		goto cleanup;
+	}
+
 	socket_t *client = socket_create(server->type);
 	if (client == NULL) {
 		ret.errno = ENOMEM;
diff --git a/kernel-src/sys/syscalls/execve.c b/kernel-src/sys/syscalls/execve.c
index 386fb69c..419f8a98 100644
--- a/kernel-src/sys/syscalls/execve.c
+++ b/kernel-src/sys/syscalls/execve.c
@@ -254,7 +254,9 @@ static syscallret_t execve(context_t *context, char *upath, char *uargv[], char
 		if (ret.errno)
 			goto error;
 
-		__assert(interpinterp == NULL);
+		if (interpinterp)
+			free(interpinterp);
+
 		VOP_RELEASE(interpnode);
 	}
 
diff --git a/kernel-src/sys/syscalls/getpid.c b/kernel-src/sys/syscalls/getpid.c
index a93569f1..9f307538 100644
--- a/kernel-src/sys/syscalls/getpid.c
+++ b/kernel-src/sys/syscalls/getpid.c
@@ -24,7 +24,13 @@ syscallret_t syscall_getpgid(context_t *ctx, pid_t pid) {
 		.errno = 0
 	};
 
-	__assert(pid == 0);
+	if (pid != 0) {
+		printf("getpgid: unsupported pid %d\n", pid);
+		ret.errno = EOPNOTSUPP;
+		ret.ret = -1;
+		return ret;
+	}
+
 	ret.ret = jobctl_getpgid(current_thread()->proc);
 	return ret;
 }
@@ -34,7 +40,13 @@ syscallret_t syscall_getsid(context_t *ctx, pid_t pid) {
 		.errno = 0
 	};
 
-	__assert(pid == 0);
+	if (pid != 0) {
+		printf("getpgid: unsupported pid %d\n", pid);
+		ret.errno = EOPNOTSUPP;
+		ret.ret = -1;
+		return ret;
+	}
+
 	ret.ret = jobctl_getsid(current_thread()->proc);
 	return ret;
 }
diff --git a/kernel-src/sys/syscalls/mmap.c b/kernel-src/sys/syscalls/mmap.c
index 7fe1259e..88ed06d5 100644
--- a/kernel-src/sys/syscalls/mmap.c
+++ b/kernel-src/sys/syscalls/mmap.c
@@ -26,11 +26,18 @@ syscallret_t syscall_mmap(context_t *context, void *hint, size_t len, int prot,
 	};
 
 	if ((~KNOWN_FLAGS & flags))
-		printf("%x\n", flags);
+		printf("mmap: unknown flags: %x\n", flags);
 
-	__assert((~KNOWN_FLAGS & flags) == 0);
-	__assert((~KNOWN_PROT & prot) == 0);
-	__assert(!((flags & MAP_PRIVATE) && (flags & MAP_SHARED)));
+	if ((~KNOWN_PROT & prot)) {
+		printf("mmap: bad prot: %x\n", prot);
+		ret.errno = EINVAL;
+		return ret;
+	}
+
+	if ((flags & MAP_PRIVATE) && (flags & MAP_SHARED)) {
+		ret.errno = EINVAL;
+		return ret;
+	}
 
 	// check alignment
 	if (len == 0 || (uintptr_t)hint % PAGE_SIZE) {
diff --git a/kernel-src/sys/syscalls/mount.c b/kernel-src/sys/syscalls/mount.c
index d5fe9846..40559562 100644
--- a/kernel-src/sys/syscalls/mount.c
+++ b/kernel-src/sys/syscalls/mount.c
@@ -19,7 +19,9 @@ syscallret_t syscall_mount(context_t *context, char *ubacking, char *umountpoint
 	syscallret_t ret = {
 		.ret = -1
 	};
-	__assert(flags == 0);
+
+	if (flags != 0)
+		printf("mount: unknown %x\n", flags);
 
 	size_t mountpointlen, fslen;
 
diff --git a/kernel-src/sys/syscalls/mprotect.c b/kernel-src/sys/syscalls/mprotect.c
index 30da37e5..616ecdd8 100644
--- a/kernel-src/sys/syscalls/mprotect.c
+++ b/kernel-src/sys/syscalls/mprotect.c
@@ -16,7 +16,10 @@ syscallret_t syscall_mprotect(context_t *context, void *address, size_t len, int
 		.ret = -1
 	};
 
-	__assert((~KNOWN_PROT & prot) == 0);
+	if (prot & ~KNOWN_PROT) {
+		ret.errno = EINVAL;
+		return ret;
+	}
 
 	// check alignment
 	if (len == 0 || (uintptr_t)address % PAGE_SIZE || address > USERSPACE_END) {
diff --git a/kernel-src/sys/syscalls/pipe2.c b/kernel-src/sys/syscalls/pipe2.c
index 51f88eda..761063d5 100644
--- a/kernel-src/sys/syscalls/pipe2.c
+++ b/kernel-src/sys/syscalls/pipe2.c
@@ -17,11 +17,13 @@ static void open(file_t *file, vnode_t *node, int flags) {
 }
 
 syscallret_t syscall_pipe2(context_t *, int flags) {
-	__assert((flags & ~(O_CLOEXEC | O_NONBLOCK)) == 0);
 	syscallret_t ret = {
 		.ret = -1
 	};
 
+	if (flags & ~(O_CLOEXEC | O_NONBLOCK))
+		printf("pipe2: unknown %x\n", flags);
+
 	vnode_t *node = NULL;
 	int readfd, writefd;
 	file_t *readfile = NULL;
diff --git a/kernel-src/sys/syscalls/recvmsg.c b/kernel-src/sys/syscalls/recvmsg.c
index af88443c..72c313f3 100644
--- a/kernel-src/sys/syscalls/recvmsg.c
+++ b/kernel-src/sys/syscalls/recvmsg.c
@@ -6,10 +6,12 @@
 #include <kernel/file.h>
 #include <kernel/alloc.h>
 
-#define KNOWN_FLAGS (MSG_PEEK | MSG_WAITALL | MSG_CMSG_CLOEXEC)
+#define KNOWN_FLAGS (MSG_PEEK | MSG_WAITALL | MSG_CMSG_CLOEXEC | MSG_DONTWAIT)
 
 syscallret_t syscall_recvmsg(context_t *, int fd, msghdr_t *umsghdr, int flags) {
-	__assert((flags & ~KNOWN_FLAGS) == 0);
+	if (flags & ~KNOWN_FLAGS)
+		printf("recvmsg: unknown %x\n", flags);
+
 	syscallret_t ret = {
 		.ret = -1
 	};
@@ -55,6 +57,9 @@ syscallret_t syscall_recvmsg(context_t *, int fd, msghdr_t *umsghdr, int flags)
 	if (flags & MSG_WAITALL)
 		recvflags |= SOCKET_RECV_FLAGS_WAITALL;
 
+	if (flags & MSG_DONTWAIT)
+		recvflags |= V_FFLAGS_NONBLOCKING;
+
 	if (flags & MSG_CMSG_CLOEXEC)
 		recvflags |= SOCKET_RECV_FLAGS_CLOEXEC_CTRL;
 
diff --git a/kernel-src/sys/syscalls/renameat.c b/kernel-src/sys/syscalls/renameat.c
index 1d613c5e..35214363 100644
--- a/kernel-src/sys/syscalls/renameat.c
+++ b/kernel-src/sys/syscalls/renameat.c
@@ -8,7 +8,8 @@ syscallret_t syscall_renameat(context_t *context, int olddirfd, char *uoldpath,
 		.ret = -1
 	};
 
-	__assert(flags == 0);
+	if (flags)
+		printf("renameat: unknown %x\n", flags);
 
 	size_t oldpathlen;
 	size_t newpathlen;
diff --git a/kernel-src/sys/syscalls/sendmsg.c b/kernel-src/sys/syscalls/sendmsg.c
index b32de3c8..24cc26a6 100644
--- a/kernel-src/sys/syscalls/sendmsg.c
+++ b/kernel-src/sys/syscalls/sendmsg.c
@@ -6,9 +6,11 @@
 #include <kernel/alloc.h>
 
 syscallret_t syscall_sendmsg(context_t *, int fd, msghdr_t *umsghdr, int flags)  {
-	__assert((flags & ~MSG_NOSIGNAL) == 0);
 	syscallret_t ret;
 
+	if (flags & ~MSG_NOSIGNAL)
+		printf("sendmsg: unknown %x\n", flags);
+
 	msghdr_t msghdr;
 	ret.errno = sock_copymsghdr(&msghdr, umsghdr);
 	if (ret.errno)
diff --git a/kernel-src/sys/syscalls/setitimer.c b/kernel-src/sys/syscalls/setitimer.c
index 55a89ebc..956ff67a 100644
--- a/kernel-src/sys/syscalls/setitimer.c
+++ b/kernel-src/sys/syscalls/setitimer.c
@@ -29,7 +29,11 @@ syscallret_t syscall_getitimer(context_t *context, int which, itimerval_t *value
 		.ret = -1
 	};
 
-	__assert(which == ITIMER_REAL);
+	if (which != ITIMER_REAL) {
+		ret.errno = EOPNOTSUPP;
+		return ret;
+	}
+
 	itimer_t *itimer = selectitimer(which);
 	if (itimer == NULL) {
 		ret.errno = EINVAL;
@@ -61,7 +65,10 @@ syscallret_t syscall_setitimer(context_t *context, int which, itimerval_t *unew,
 		.ret = -1
 	};
 
-	__assert(which == ITIMER_REAL);
+	if (which != ITIMER_REAL) {
+		ret.errno = EOPNOTSUPP;
+		return ret;
+	}
 
 	itimer_t *itimer = selectitimer(which);
 	if (itimer == NULL) {
diff --git a/kernel-src/sys/syscalls/waitpid.c b/kernel-src/sys/syscalls/waitpid.c
index 15069dff..899b23d7 100644
--- a/kernel-src/sys/syscalls/waitpid.c
+++ b/kernel-src/sys/syscalls/waitpid.c
@@ -15,9 +15,14 @@ syscallret_t syscall_waitpid(context_t *context, pid_t pid, int *status, int opt
 		.ret = -1
 	};
 
-	__assert((options & ~KNOWN_FLAGS) == 0);
-	// TODO implement these
-	__assert(pid == -1 || pid > 0);
+	if (options & ~KNOWN_FLAGS)
+		printf("waitpid: unknown %x\n", options);
+
+	if (pid < -1 || pid == 0) {
+		printf("waitpid: unhandled pid %d\n", pid);
+		ret.errno = EOPNOTSUPP;
+		return ret;
+	}
 
 	thread_t *thread = current_thread();
 	proc_t *proc = thread->proc;