diff --git a/libmaxsi/c/hsrc/unistd.h b/libmaxsi/c/hsrc/unistd.h
index 6844a588..6cb2f206 100644
--- a/libmaxsi/c/hsrc/unistd.h
+++ b/libmaxsi/c/hsrc/unistd.h
@@ -112,7 +112,6 @@ pid_t getpgid(pid_t);
 pid_t getpgrp(void);
 pid_t getsid(pid_t);
 uid_t getuid(void);
-int isatty(int);
 int lchown(const char*, uid_t, gid_t);
 int link(const char*, const char*);
 int linkat(int, const char*, int, const char*, int);
@@ -162,6 +161,7 @@ pid_t fork(void);
 char* getcwd(char*, size_t);
 pid_t getpid(void);
 pid_t getppid(void);
+int isatty(int);
 int pipe(int [2]);
 ssize_t read(int, void*, size_t);
 unsigned sleep(unsigned);
diff --git a/libmaxsi/decl/errno_values.h b/libmaxsi/decl/errno_values.h
index 08a39af8..a8bf3095 100644
--- a/libmaxsi/decl/errno_values.h
+++ b/libmaxsi/decl/errno_values.h
@@ -20,5 +20,6 @@
 #define ENOEXEC 28
 #define EACCESS 29
 #define ESRCH 30
+#define ENOTTY 31
 
 #endif
diff --git a/libmaxsi/error.cpp b/libmaxsi/error.cpp
index b3f4cdd8..7aabd5a7 100644
--- a/libmaxsi/error.cpp
+++ b/libmaxsi/error.cpp
@@ -63,6 +63,7 @@ namespace Maxsi
 				case ENOEXEC: return (char*) "Not executable";
 				case EACCESS: return (char*) "Permission denied";
 				case ESRCH: return (char*) "No such process";
+				case ENOTTY: return (char*) "Not a tty";
 				default: return (char*) "Unknown error condition";
 			}
 		}
diff --git a/libmaxsi/io.cpp b/libmaxsi/io.cpp
index db95beb6..a7318240 100644
--- a/libmaxsi/io.cpp
+++ b/libmaxsi/io.cpp
@@ -47,6 +47,7 @@ namespace Maxsi
 	DEFN_SYSCALL1(int, SysChDir, 25, const char*);
 	DEFN_SYSCALL2(char*, SysGetCWD, 26, char*, size_t);
 	DEFN_SYSCALL1(int, SysUnlink, 27, const char*);
+	DEFN_SYSCALL1(int, SysIsATTY, 33, int);
 
 	size_t Print(const char* string)
 	{
@@ -161,6 +162,11 @@ namespace Maxsi
 	{
 		return SysUnlink(pathname);
 	}
+
+	extern "C" int isatty(int fd)
+	{
+		return SysIsATTY(fd);
+	}
 #endif
 
 }
diff --git a/sortix/device.h b/sortix/device.h
index 591f61f9..477d56ce 100644
--- a/sortix/device.h
+++ b/sortix/device.h
@@ -35,6 +35,7 @@ namespace Sortix
 		static const unsigned VGABUFFER = 2;
 		static const unsigned FILESYSTEM = 3;
 		static const unsigned DIRECTORY = 4;
+		static const unsigned TTY = 5;
 
 	public:
 		Device();
diff --git a/sortix/fs/ramfs.cpp b/sortix/fs/ramfs.cpp
index 08275590..0879db4f 100644
--- a/sortix/fs/ramfs.cpp
+++ b/sortix/fs/ramfs.cpp
@@ -51,6 +51,7 @@ namespace Sortix
 	private:
 		size_t offset;
 		byte* buffer;
+		size_t bufferused;
 		size_t buffersize;
 
 	public:
@@ -70,6 +71,7 @@ namespace Sortix
 	{
 		this->name = name;
 		buffer = NULL;
+		bufferused = 0;
 		buffersize = 0;
 	}
 
@@ -86,7 +88,7 @@ namespace Sortix
 
 	uintmax_t DevRAMFSFile::Size()
 	{
-		return buffersize;
+		return bufferused;
 	}
 
 	uintmax_t DevRAMFSFile::Position()
@@ -106,10 +108,11 @@ namespace Sortix
 		if ( SIZE_MAX < size ) { Error::Set(EOVERFLOW); return false; }
 		byte* newbuffer = new byte[size];
 		if ( !newbuffer ) { Error::Set(ENOSPC); return false; }
-		size_t sharedmemsize = ( size < buffersize ) ? size : buffersize;
+		size_t sharedmemsize = ( size < bufferused ) ? size : bufferused;
 		Memory::Copy(newbuffer, buffer, sharedmemsize);
 		delete[] buffer;
 		buffer = newbuffer;
+		bufferused = sharedmemsize;
 		buffersize = size;
 		return true;
 	}
@@ -118,7 +121,7 @@ namespace Sortix
 	{
 		if ( SSIZE_MAX < count ) { count = SSIZE_MAX; }
 		size_t available = count;
-		if ( buffersize < offset + count ) { available = buffersize - offset; }
+		if ( bufferused < offset + count ) { available = bufferused - offset; }
 		if ( available == 0 ) { return 0; }
 		Memory::Copy(dest, buffer + offset, available);
 		offset += available;
@@ -137,6 +140,7 @@ namespace Sortix
 
 		Memory::Copy(buffer + offset, src, count);
 		offset += count;
+		if ( bufferused < offset ) { bufferused = offset; }
 		return count;
 	}
 
diff --git a/sortix/io.cpp b/sortix/io.cpp
index 96ed233a..c42d9521 100644
--- a/sortix/io.cpp
+++ b/sortix/io.cpp
@@ -52,13 +52,13 @@ namespace Sortix
 			if ( SSIZE_MAX < count ) { count = SSIZE_MAX; }
 			Process* process = CurrentProcess();
 			Device* dev = process->descriptors.Get(fd);
-			if ( !dev ) { return -1; /* TODO: EBADF */ }
-			if ( !dev->IsType(Device::STREAM) ) { return -1; /* TODO: EBADF */ }
+			if ( !dev ) { Error::Set(EBADF); return -1; }
+			if ( !dev->IsType(Device::STREAM) ) { Error::Set(EBADF); return -1; }
 			DevStream* stream = (DevStream*) dev;
-			if ( !stream->IsWritable() ) { return -1; /* TODO: EBADF */ }
+			if ( !stream->IsWritable() ) { Error::Set(EBADF); return -1; }
 			ssize_t written = stream->Write(buffer, count);
 			if ( 0 <= written ) { return written; }
-			if ( Error::Last() != EWOULDBLOCK ) { return -1; /* TODO: errno */ }
+			if ( Error::Last() != EWOULDBLOCK ) { return -1; }
 
 			// The stream will resume our system call once progress has been
 			// made. Our request is certainly not forgotten.
@@ -92,13 +92,13 @@ namespace Sortix
 			if ( SSIZE_MAX < count ) { count = SSIZE_MAX; }
 			Process* process = CurrentProcess();
 			Device* dev = process->descriptors.Get(fd);
-			if ( !dev ) { return -1; /* TODO: EBADF */ }
-			if ( !dev->IsType(Device::STREAM) ) { return -1; /* TODO: EBADF */ }
+			if ( !dev ) { Error::Set(EBADF); return -1; }
+			if ( !dev->IsType(Device::STREAM) ) { Error::Set(EBADF); return -1; }
 			DevStream* stream = (DevStream*) dev;
-			if ( !stream->IsReadable() ) { return -1; /* TODO: EBADF */ }
+			if ( !stream->IsReadable() ) { Error::Set(EBADF); return -1;}
 			ssize_t bytesread = stream->Read(buffer, count);
 			if ( 0 <= bytesread ) { return bytesread; }
-			if ( Error::Last() != EWOULDBLOCK ) { return -1; /* TODO: errno */ }
+			if ( Error::Last() != EWOULDBLOCK ) { return -1; }
 
 			// The stream will resume our system call once progress has been
 			// made. Our request is certainly not forgotten.
@@ -121,7 +121,7 @@ namespace Sortix
 		{
 			Process* process = CurrentProcess();
 			Device* dev = process->descriptors.Get(fd);
-			if ( !dev ) { return -1; /* TODO: EBADF */ }
+			if ( !dev ) { Error::Set(EBADF); return -1; }
 			process->descriptors.Free(fd);
 			return 0;
 		}
@@ -130,16 +130,26 @@ namespace Sortix
 		{
 			Process* process = CurrentProcess();
 			Device* dev = process->descriptors.Get(fd);
-			if ( !dev ) { return -1; /* TODO: EBADF */ }
+			if ( !dev ) { Error::Set(EBADF); return -1; }
 			return process->descriptors.Allocate(dev);
 		}
 
+		int SysIsATTY(int fd)
+		{
+			Process* process = CurrentProcess();
+			Device* dev = process->descriptors.Get(fd);
+			if ( !dev ) { Error::Set(EBADF); return 0; }
+			if ( !dev->IsType(Device::TTY) ) {  Error::Set(ENOTTY); return 0; }
+			return 1;
+		}
+
 		void Init()
 		{
 			Syscall::Register(SYSCALL_WRITE, (void*) SysWrite);
 			Syscall::Register(SYSCALL_READ, (void*) SysRead);
 			Syscall::Register(SYSCALL_CLOSE, (void*) SysClose);
 			Syscall::Register(SYSCALL_DUP, (void*) SysDup);
+			Syscall::Register(SYSCALL_ISATTY, (void*) SysIsATTY);
 		}
 	}
 }
diff --git a/sortix/syscallnum.h b/sortix/syscallnum.h
index 485a413b..9b458fb1 100644
--- a/sortix/syscallnum.h
+++ b/sortix/syscallnum.h
@@ -58,7 +58,8 @@
 #define SYSCALL_SIGRETURN 30
 #define SYSCALL_KILL 31
 #define SYSCALL_MEMSTAT 32
-#define SYSCALL_MAX_NUM 33 /* index of highest constant + 1 */
+#define SYSCALL_ISATTY 33
+#define SYSCALL_MAX_NUM 34 /* index of highest constant + 1 */
 
 #endif
 
diff --git a/utils/editor.cpp b/utils/editor.cpp
index bbca7b5c..65165718 100644
--- a/utils/editor.cpp
+++ b/utils/editor.cpp
@@ -410,6 +410,8 @@ void run()
 
 int main(int argc, char* argv[])
 {
+	if ( !isatty(1) ) { error(1, errno, "stdout must be a tty"); return 1; }
+
 	if ( argc < 2 )
 	{
 		clearbuffers();