diff --git a/src/lib/os/env.go b/src/lib/os/env.go
index 4c53a9a..69af223 100644
--- a/src/lib/os/env.go
+++ b/src/lib/os/env.go
@@ -11,11 +11,11 @@
 	"os";
 )
 
-var (
-	ENOENV = NewError("no such environment variable");
+// ENOENV is the Error indicating that an environment variable does not exist.
+var ENOENV = NewError("no such environment variable");
 
-	env map[string] string;
-)
+var env map[string] string;
+
 
 func copyenv() {
 	env = make(map[string] string);
@@ -29,6 +29,8 @@
 	}
 }
 
+// Getenv retrieves the value of the environment variable named by the key.
+// It returns the value and an error, if any.
 func Getenv(key string) (value string, err *Error) {
 	once.Do(copyenv);
 
@@ -42,6 +44,8 @@
 	return v, nil;
 }
 
+// Setenv sets the value of the environment variable named by the key.
+// It returns an Error, if any.
 func Setenv(key, value string) *Error {
 	once.Do(copyenv);
 
@@ -52,11 +56,14 @@
 	return nil;
 }
 
+// Clearenv deletes all environment variables.
 func Clearenv() {
 	once.Do(copyenv);	// prevent copyenv in Getenv/Setenv
 	env = make(map[string] string);
 }
 
+// Environ returns an array of strings representing the environment,
+// in the form "key=value".
 func Environ() []string {
 	once.Do(copyenv);
 	a := make([]string, len(env));
diff --git a/src/lib/os/error.go b/src/lib/os/error.go
index 63b2dbc..18d010c 100644
--- a/src/lib/os/error.go
+++ b/src/lib/os/error.go
@@ -6,8 +6,12 @@
 
 import syscall "syscall"
 
-// Errors are singleton structures. Use the String() method to get their contents --
-// it handles the nil (no error) case.
+// Error is a structure wrapping a string describing an error.
+// Errors are singleton structures, created by NewError, so their addresses can
+// be compared to test for equality. A nil Error pointer means ``no error''.
+// Use the String() method to get the contents; it handles the nil case.
+// The Error type is intended for use by any package that wishes to define
+// error strings.
 type Error struct {
 	s string
 }
@@ -24,7 +28,8 @@
 // These functions contain a race if two goroutines add identical
 // errors simultaneously but the consequences are unimportant.
 
-// Allocate an Error object, but if it's been seen before, share that one.
+// NewError allocates an Error object, but if s has been seen before,
+// shares the Error associated with that message.
 func NewError(s string) *Error {
 	if s == "" {
 		return nil
@@ -38,7 +43,8 @@
 	return err;
 }
 
-// Allocate an Error objecct, but if it's been seen before, share that one.
+// ErrnoToError calls NewError to create an Error object for the string
+// associated with Unix error code errno.
 func ErrnoToError(errno int64) *Error {
 	if errno == 0 {
 		return nil
@@ -53,6 +59,7 @@
 	return err;
 }
 
+// Commonly known Unix errors.
 var (
 	ENONE = ErrnoToError(syscall.ENONE);
 	EPERM = ErrnoToError(syscall.EPERM);
@@ -92,6 +99,7 @@
 	EAGAIN = ErrnoToError(syscall.EAGAIN);
 )
 
+// String returns the string associated with the Error.
 func (e *Error) String() string {
 	if e == nil {
 		return "No Error"
diff --git a/src/lib/os/exec.go b/src/lib/os/exec.go
index 44e70cb..b16a6c4 100644
--- a/src/lib/os/exec.go
+++ b/src/lib/os/exec.go
@@ -9,6 +9,12 @@
 	"syscall";
 )
 
+// ForkExec forks the current process and invokes Exec with the file, arguments,
+// and environment specified by argv0, argv, and envv.  It returns the process
+// id of the forked process and an Error, if any.  The fd array specifies the
+// file descriptors to be set up in the new process: fd[0] will be Unix file
+// descriptor 0 (standard input), fd[1] descriptor 1, and so on.  A nil entry
+// will cause the child to have no open file descriptor with that index.
 func ForkExec(argv0 string, argv []string, envv []string, fd []*FD)
 	(pid int, err *Error)
 {
@@ -26,6 +32,10 @@
 	return int(p), ErrnoToError(e);
 }
 
+// Exec replaces the current process with an execution of the program
+// named by argv0, with arguments argv and environment envv.
+// If successful, Exec never returns.  If it fails, it returns an Error.
+// ForkExec is almost always a better way to execute a program.
 func Exec(argv0 string, argv []string, envv []string) *Error {
 	if envv == nil {
 		envv = Environ();
@@ -41,18 +51,24 @@
 // since syscall one might have different field types across
 // different OS.
 
+// Waitmsg stores the information about an exited process as reported by Wait.
 type Waitmsg struct {
-	Pid int;
-	syscall.WaitStatus;
-	Rusage *syscall.Rusage;
+	Pid int;	// The process's id.
+	syscall.WaitStatus;	// System-dependent status info.
+	Rusage *syscall.Rusage;	// System-dependent resource usage info.
 }
 
+// Options for Wait.
 const (
-	WNOHANG = syscall.WNOHANG;
-	WSTOPPED = syscall.WSTOPPED;
-	WRUSAGE = 1<<60;
+	WNOHANG = syscall.WNOHANG;	// Don't wait if no process has exited.
+	WSTOPPED = syscall.WSTOPPED;	// If set, status of stopped subprocesses is also reported.
+	WUNTRACED = WSTOPPED;
+	WRUSAGE = 1<<60;	// Record resource usage.
 )
 
+// Wait waits for process pid to exit or stop, and then returns a
+// Waitmsg describing its status and an Error, if any. The options
+// (WNOHANG etc.) affect the behavior of the Wait call.
 func Wait(pid int, options uint64) (w *Waitmsg, err *Error) {
 	var status syscall.WaitStatus;
 	var rusage *syscall.Rusage;
diff --git a/src/lib/os/file.go b/src/lib/os/file.go
index b41f241..1fb2a64 100644
--- a/src/lib/os/file.go
+++ b/src/lib/os/file.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// The os package provides a platform-independent interface to operating
+// system functionality.  The design is Unix-like.
 package os
 
 import (
@@ -16,21 +18,25 @@
 	bufp	int64;	// location of next record in buf.
 }
 
-// FDs are wrappers for file descriptors
+// FD represents an open file.
+// TODO(r): is FD the right name? Would File be better?
 type FD struct {
 	fd int64;
 	name	string;
 	dirinfo	*dirInfo;	// nil unless directory being read
 }
 
+// Fd returns the integer Unix file descriptor referencing the open file.
 func (fd *FD) Fd() int64 {
 	return fd.fd
 }
 
+// Name returns the name of the file as presented to Open.
 func (fd *FD) Name() string {
 	return fd.name
 }
 
+// NewFD returns a new FD with the given file descriptor and name.
 func NewFD(fd int64, name string) *FD {
 	if fd < 0 {
 		return nil
@@ -38,28 +44,35 @@
 	return &FD{fd, name, nil}
 }
 
+// Stdin, Stdout, and Stderr are open FDs pointing to the standard input,
+// standard output, and standard error file descriptors.
 var (
 	Stdin = NewFD(0, "/dev/stdin");
 	Stdout = NewFD(1, "/dev/stdout");
 	Stderr = NewFD(2, "/dev/stderr");
 )
 
+// Flags to Open wrapping those of the underlying system. Not all flags
+// may be implemented on a given system.
 const (
-	O_RDONLY = syscall.O_RDONLY;
-	O_WRONLY = syscall.O_WRONLY;
-	O_RDWR = syscall.O_RDWR;
-	O_APPEND = syscall.O_APPEND;
-	O_ASYNC = syscall.O_ASYNC;
-	O_CREAT = syscall.O_CREAT;
-	O_NOCTTY = syscall.O_NOCTTY;
-	O_NONBLOCK = syscall.O_NONBLOCK;
-	O_NDELAY = O_NONBLOCK;
-	O_SYNC = syscall.O_SYNC;
-	O_TRUNC = syscall.O_TRUNC;
+	O_RDONLY = syscall.O_RDONLY;	// open the file read-only.
+	O_WRONLY = syscall.O_WRONLY;	// open the file write-only.
+	O_RDWR = syscall.O_RDWR;	// open the file read-write.
+	O_APPEND = syscall.O_APPEND;	// open the file append-only.
+	O_ASYNC = syscall.O_ASYNC;	// generate a signal when I/O is available.
+	O_CREAT = syscall.O_CREAT;	// create a new file if none exists.
+	O_NOCTTY = syscall.O_NOCTTY;	// do not make file the controlling tty.
+	O_NONBLOCK = syscall.O_NONBLOCK;	// open in non-blocking mode.
+	O_NDELAY = O_NONBLOCK;		// synonym for O_NONBLOCK
+	O_SYNC = syscall.O_SYNC;	// open for synchronous I/O.
+	O_TRUNC = syscall.O_TRUNC;	// if possible, truncate file when opened.
 )
 
-func Open(name string, mode int, flags int) (fd *FD, err *Error) {
-	r, e := syscall.Open(name, int64(mode), int64(flags | syscall.O_CLOEXEC));
+// Open opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.)
+// if applicable.  If successful, methods on the returned FD can be used for I/O.
+// It returns the FD and an Error, if any.
+func Open(name string, flag int, perm int) (fd *FD, err *Error) {
+	r, e := syscall.Open(name, int64(flag | syscall.O_CLOEXEC), int64(perm));
 	if e != 0 {
 		return nil, ErrnoToError(e);
 	}
@@ -73,6 +86,8 @@
 	return NewFD(r, name), ErrnoToError(e)
 }
 
+// Close closes the FD, rendering it unusable for I/O.
+// It returns an Error, if any.
 func (fd *FD) Close() *Error {
 	if fd == nil {
 		return EINVAL
@@ -82,6 +97,10 @@
 	return ErrnoToError(e)
 }
 
+// Read reads up to len(b) bytes from the FD.
+// It returns the number of bytes read and an Error, if any.
+// EOF is signaled by a zero count with a nil Error.
+// TODO(r): Add Pread, Pwrite (maybe ReadAt, WriteAt).
 func (fd *FD) Read(b []byte) (ret int, err *Error) {
 	if fd == nil {
 		return 0, EINVAL
@@ -96,6 +115,9 @@
 	return int(r), ErrnoToError(e)
 }
 
+// Write writes len(b) bytes to the FD.
+// It returns the number of bytes written and an Error, if any.
+// If the byte count differs from len(b), it usually implies an error occurred.
 func (fd *FD) Write(b []byte) (ret int, err *Error) {
 	if fd == nil {
 		return 0, EINVAL
@@ -110,6 +132,10 @@
 	return int(r), ErrnoToError(e)
 }
 
+// Seek sets the offset for the next Read or Write on FD to offset, interpreted
+// according to whence: 0 means relative to the origin of the file, 1 means
+// relative to the current offset, and 2 means relative to the end.
+// It returns the new offset and an Error, if any.
 func (fd *FD) Seek(offset int64, whence int) (ret int64, err *Error) {
 	r, e := syscall.Seek(fd.fd, offset, int64(whence));
 	if e != 0 {
@@ -121,6 +147,8 @@
 	return r, nil
 }
 
+// WriteString is like Write, but writes the contents of string s rather than
+// an array of bytes.
 func (fd *FD) WriteString(s string) (ret int, err *Error) {
 	if fd == nil {
 		return 0, EINVAL
@@ -132,12 +160,14 @@
 	return int(r), ErrnoToError(e)
 }
 
-func Pipe() (fd1 *FD, fd2 *FD, err *Error) {
+// Pipe returns a connected pair of FDs; reads from r return bytes written to w.
+// It returns the FDs and an Error, if any.
+func Pipe() (r *FD, w *FD, err *Error) {
 	var p [2]int64;
 
 	// See ../syscall/exec.go for description of lock.
 	syscall.ForkLock.RLock();
-	r, e := syscall.Pipe(&p);
+	ret, e := syscall.Pipe(&p);
 	if e != 0 {
 		syscall.ForkLock.RUnlock();
 		return nil, nil, ErrnoToError(e)
@@ -149,11 +179,17 @@
 	return NewFD(p[0], "|0"), NewFD(p[1], "|1"), nil
 }
 
+// Mkdir creates a new directory with the specified name and permission bits.
+// It returns an error, if any.
 func Mkdir(name string, perm int) *Error {
 	r, e := syscall.Mkdir(name, int64(perm));
 	return ErrnoToError(e)
 }
 
+// Stat returns the Dir structure describing the named file. If the file
+// is a symbolic link, it returns information about the file the link
+// references.
+// It returns the Dir and an error, if any.
 func Stat(name string) (dir *Dir, err *Error) {
 	stat := new(syscall.Stat_t);
 	r, e := syscall.Stat(name, stat);
@@ -163,6 +199,8 @@
 	return dirFromStat(name, new(Dir), stat), nil
 }
 
+// Fstat returns the Dir structure describing the file associated with the FD.
+// It returns the Dir and an error, if any.
 func Fstat(fd *FD) (dir *Dir, err *Error) {
 	stat := new(syscall.Stat_t);
 	r, e := syscall.Fstat(fd.fd, stat);
@@ -172,6 +210,9 @@
 	return dirFromStat(fd.name, new(Dir), stat), nil
 }
 
+// Lstat returns the Dir structure describing the named file. If the file
+// is a symbolic link, it returns information about the link itself.
+// It returns the Dir and an error, if any.
 func Lstat(name string) (dir *Dir, err *Error) {
 	stat := new(syscall.Stat_t);
 	r, e := syscall.Lstat(name, stat);
@@ -181,10 +222,21 @@
 	return dirFromStat(name, new(Dir), stat), nil
 }
 
-// Non-portable function defined in operating-system-dependent file.
+// Readdirnames has a non-portable implemenation so its code is separated into an
+// operating-system-dependent file.
+
+// Readdirnames reads the contents of the directory associated with fd and
+// returns an array of up to count names, in directory order.  Subsequent
+// calls on the same fd will yield further names.
+// A negative count means to read until EOF.
+// It returns the array and an Error, if any.
 func Readdirnames(fd *FD, count int) (names []string, err *os.Error)
 
-// Negative count means read until EOF.
+// Readdir reads the contents of the directory associated with fd and
+// returns an array of up to count Dir structures, in directory order.  Subsequent
+// calls on the same fd will yield further Dirs.
+// A negative count means to read until EOF.
+// It returns the array and an Error, if any.
 func Readdir(fd *FD, count int) (dirs []Dir, err *os.Error) {
 	dirname := fd.name;
 	if dirname == "" {
diff --git a/src/lib/os/time.go b/src/lib/os/time.go
index 0f5fdfd..9847d80 100644
--- a/src/lib/os/time.go
+++ b/src/lib/os/time.go
@@ -9,6 +9,11 @@
 	"syscall"
 )
 
+
+// Time returns the current time, in whole seconds and
+// fractional nanoseconds, plus an Error if any. The current
+// time is thus 1e9*sec+nsec, in nanoseconds.  The zero of
+// time is the Unix epoch.
 func Time() (sec int64, nsec int64, err *Error) {
 	var errno int64;
 	sec, nsec, errno = syscall.Gettimeofday();
diff --git a/src/lib/os/types.go b/src/lib/os/types.go
index 5157dca..aba4631 100644
--- a/src/lib/os/types.go
+++ b/src/lib/os/types.go
@@ -9,52 +9,60 @@
 // An operating-system independent representation of Unix data structures.
 // OS-specific routines in this directory convert the OS-local versions to these.
 
-// Result of stat64(2) etc.
+// A Dir describes a file and is returned by Stat, Fstat, and Lstat
 type Dir struct {
-	Dev	uint64;
-	Ino	uint64;
-	Nlink	uint64;
-	Mode	uint32;
-	Uid	uint32;
-	Gid	uint32;
-	Rdev	uint64;
-	Size	uint64;
-	Blksize	uint64;
-	Blocks	uint64;
-	Atime_ns	uint64;	// nanoseconds since 1970
-	Mtime_ns	uint64;	// nanoseconds since 1970
-	Ctime_ns	uint64;	// nanoseconds since 1970
-	Name	string;
+	Dev	uint64;	// device number of file system holding file.
+	Ino	uint64;	// inode number.
+	Nlink	uint64;	// number of hard links.
+	Mode	uint32;	// permission and mode bits.
+	Uid	uint32;	// user id of owner.
+	Gid	uint32;	// group id of owner.
+	Rdev	uint64;	// device type for special file.
+	Size	uint64;	// length in bytes.
+	Blksize	uint64;	// size of blocks, in bytes.
+	Blocks	uint64;	// number of blocks allocated for file.
+	Atime_ns	uint64;	// access time; nanoseconds since epoch.
+	Mtime_ns	uint64;	// modified time; nanoseconds since epoch.
+	Ctime_ns	uint64;	// status change time; nanoseconds since epoch.
+	Name	string;	// name of file as presented to Open.
 }
 
+// IsFifo reports whether the Dir describes a FIFO file.
 func (dir *Dir) IsFifo() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFIFO
 }
 
+// IsChar reports whether the Dir describes a character special file.
 func (dir *Dir) IsChar() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFCHR
 }
 
+// IsDirectory reports whether the Dir describes a directory.
 func (dir *Dir) IsDirectory() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFDIR
 }
 
+// IsBlock reports whether the Dir describes a block special file.
 func (dir *Dir) IsBlock() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFBLK
 }
 
+// IsRegular reports whether the Dir describes a regular file.
 func (dir *Dir) IsRegular() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFREG
 }
 
+// IsSymlink reports whether the Dir describes a symbolic link.
 func (dir *Dir) IsSymlink() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFLNK
 }
 
+// IsSocket reports whether the Dir describes a socket.
 func (dir *Dir) IsSocket() bool {
 	return (dir.Mode & syscall.S_IFMT) == syscall.S_IFSOCK
 }
 
+// Permission returns the file permission bits.
 func (dir *Dir) Permission() int {
 	return int(dir.Mode & 0777)
 }