diff --git a/doc/user-guide b/doc/user-guide
index 6118d3b8..fb42f216 100644
--- a/doc/user-guide
+++ b/doc/user-guide
@@ -145,6 +145,7 @@ Sortix comes with a number of home-made programs. Here is an overview:
 * `benchsyscall` - slightly less useless benchmark
 * `calc` - reverse polish calculator
 * `cat` - display file on terminal
+* `chmod` - change file mode bits
 * `chroot` - change the root directory
 * `chvideomode` - change display resolution
 * `clear` - clear terminal
diff --git a/utils/.gitignore b/utils/.gitignore
index b75d749f..e887dca8 100644
--- a/utils/.gitignore
+++ b/utils/.gitignore
@@ -1,6 +1,7 @@
 *.o
 calc
 cat
+chmod
 chroot
 chvideomode
 clear
diff --git a/utils/Makefile b/utils/Makefile
index 4429779f..85dc7a91 100644
--- a/utils/Makefile
+++ b/utils/Makefile
@@ -17,6 +17,7 @@ CXXFLAGS:=$(CXXFLAGS) -Wall -Wextra -fno-exceptions -fno-rtti
 BINARIES:=\
 calc \
 cat \
+chmod \
 chroot \
 chvideomode \
 clear \
diff --git a/utils/chmod.cpp b/utils/chmod.cpp
new file mode 100644
index 00000000..c357ec5c
--- /dev/null
+++ b/utils/chmod.cpp
@@ -0,0 +1,426 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2014.
+
+    This program is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    This program is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+    more details.
+
+    You should have received a copy of the GNU General Public License along with
+    this program. If not, see <http://www.gnu.org/licenses/>.
+
+    chmod.cpp
+    Change file mode bits.
+
+*******************************************************************************/
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <assert.h>
+#include <dirent.h>
+#include <errno.h>
+#include <error.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static const int FLAG_CHANGES = 1 << 0;
+static const int FLAG_VERBOSE = 1 << 1;
+static const int FLAG_RECURSIVE = 1 << 2;
+
+enum symderef
+{
+	SYMDEREF_NONE,
+	SYMDEREF_ARGUMENTS,
+	SYMDEREF_ALWAYS,
+	SYMDEREF_DEFAULT,
+};
+
+static bool is_octal_string(const char* str)
+{
+	if ( !str[0] )
+		return false;
+	for ( size_t i = 0; str[i]; i++ )
+		if ( !('0' <= str[i] && str[i] <= '7') )
+			return false;
+	return true;
+}
+
+static mode_t execute_modespec(const char* str,
+                               mode_t mode,
+                               mode_t type,
+                               mode_t umask)
+{
+	if ( is_octal_string(str) )
+	{
+		errno = 0;
+		uintmax_t input = strtoumax((char*) str, NULL, 8);
+		if ( errno == ERANGE )
+			return (mode_t) -1;
+		if ( input & ~((uintmax_t) 07777) )
+			return (mode_t) -1;
+		return (mode_t) input;
+	}
+
+	size_t index = 0;
+	do
+	{
+		mode_t who_mask = 01000;
+		while ( true )
+		{
+			if ( str[index] == 'u' && (index++, true) )
+				who_mask |= 04700;
+			else if ( str[index] == 'g' && (index++, true) )
+				who_mask |= 02070;
+			else if ( str[index] == 'o' && (index++, true) )
+				who_mask |= 00007;
+			else if ( str[index] == 'a' && (index++, true) )
+				who_mask |= 06777;
+			else
+				break;
+		}
+		if ( !(who_mask & 0777) )
+			who_mask |= 06777 & ~umask;
+		do
+		{
+			char op;
+			switch ( (op = str[index++]) )
+			{
+			case '+': break;
+			case '-': break;
+			case '=': break;
+			default: return (mode_t) -1;
+			};
+			mode_t operand = 0;
+			if ( str[index] == 'u' || str[index] == 'g' || str[index] == 'o' )
+			{
+				char permcopy = str[index++];
+				switch ( permcopy )
+				{
+				case 'u': operand = mode >> 6 & 07; break;
+				case 'g': operand = mode >> 3 & 07; break;
+				case 'o': operand = mode >> 0 & 07; break;
+				default: __builtin_unreachable();
+				};
+				operand = operand << 0 | operand << 3 | operand << 6;
+				switch ( permcopy )
+				{
+				case 'u': if ( mode & 04000) operand |= 06000; break;
+				case 'g': if ( mode & 02000) operand |= 06000; break;
+				};
+				who_mask &= ~((mode_t) 01000);
+			}
+			else
+			{
+				bool unknown = false;
+				do
+				{
+					switch ( str[index] )
+					{
+					case 'r': operand |= 00444; break;
+					case 'w': operand |= 00222; break;
+					case 'x': operand |= 00111; break;
+					case 'X':
+						if ( S_ISDIR(type) || (mode & 0111) )
+							operand |= 00111;
+						break;
+					case 's': operand |= 06000; break;
+					case 't': operand |= 00000; break;
+					default: unknown = true; break;
+					}
+				} while ( !unknown && (index++, true) );
+			}
+			switch ( op )
+			{
+			case '+': mode |= (operand & who_mask); break;
+			case '-': mode &= ~(operand & who_mask); break;
+			case '=': mode = (mode & ~who_mask) | (operand & who_mask); break;
+			default: __builtin_unreachable();
+			}
+		} while ( str[index] == '+' ||
+		          str[index] == '-' ||
+		          str[index] == '=' );
+	} while ( str[index] == ',' && (index++, true) );
+	if ( str[index] )
+		return (mode_t) -1;
+	return mode;
+}
+
+static bool is_valid_modespec(const char* str)
+{
+	return execute_modespec(str, 0, 0, 0) != (mode_t) -1;
+}
+
+static bool do_chmod_directory(int fd,
+                               const char* path,
+                               const char* modespec,
+                               int flags,
+                               enum symderef symderef);
+
+static bool do_chmod(int dirfd,
+                     const char* relpath,
+                     const char* path,
+                     const char* modespec,
+                     int flags,
+                     enum symderef symderef)
+{
+	bool success = true;
+
+	int fd_open_flags = O_RDONLY;
+	if ( symderef == SYMDEREF_NONE )
+		fd_open_flags |= O_SYMLINK_NOFOLLOW;
+	int fd = openat(dirfd, relpath, fd_open_flags);
+	if ( fd < 0 )
+	{
+		error(0, errno, "`%s'", path);
+		return false;
+	}
+
+	struct stat st;
+	if ( fstat(fd, &st) < 0 )
+	{
+		error(0, errno, "stat: `%s'", path);
+		close(fd);
+		return false;
+	}
+
+	if ( S_ISLNK(st.st_mode) )
+	{
+		close(fd);
+		return true;
+	}
+
+	mode_t old_mode = st.st_mode & 07777;
+	mode_t new_mode = execute_modespec(modespec, old_mode, st.st_mode, getumask());
+	assert(new_mode != (mode_t) -1);
+
+	if ( fchmod(fd, new_mode) < 0 )
+	{
+		error(0, errno, "changing permissions: `%s'", path);
+		success = false;
+	}
+	else
+	{
+		mode_t naive_mode = execute_modespec(modespec, old_mode, st.st_mode, 0);
+		assert(naive_mode != (mode_t) -1);
+
+		if ( new_mode & ~naive_mode )
+			error(0, 0, "%s: new permissions are %jo, not %jo",
+			            path, (uintmax_t) new_mode, (uintmax_t) naive_mode);
+
+		if ( (flags & FLAG_VERBOSE) ||
+			 (old_mode != new_mode && (flags & FLAG_CHANGES)) )
+		{
+			if ( old_mode == new_mode )
+				printf("mode of `%s' retained as %jo\n",
+					   path, (uintmax_t) new_mode);
+			else
+				printf("mode of `%s' changed from %jo to %jo\n",
+					   path, (uintmax_t) old_mode, (uintmax_t) new_mode);
+		}
+	}
+
+	if ( S_ISDIR(st.st_mode) && (flags & FLAG_RECURSIVE) )
+	{
+		if ( !do_chmod_directory(fd, path, modespec, flags, symderef) )
+			success = false;
+	}
+
+	close(fd);
+	return success;
+}
+
+static bool do_chmod_directory(int fd,
+                               const char* path,
+                               const char* modespec,
+                               int flags,
+                               enum symderef symderef)
+{
+	if ( symderef == SYMDEREF_ARGUMENTS )
+		symderef = SYMDEREF_NONE;
+
+	int fd_copy = dup(fd);
+	if ( fd_copy < 0 )
+	{
+		error(0, errno, "dup: `%s'", path);
+		return false;
+	}
+
+	DIR* dir = fdopendir(fd_copy);
+	if ( !dir )
+	{
+		error(0, errno, "fdopendir: `%s'", path);
+		close(fd_copy);
+		return false;
+	}
+
+	const char* joiner = "/";
+	size_t path_length = strlen(path);
+	if ( path_length && path[path_length - 1] == '/' )
+		joiner = "";
+
+	bool success = true;
+	while ( struct dirent* entry = readdir(dir) )
+	{
+		if ( !strcmp(entry->d_name, ".") || !strcmp(entry->d_name, "..") )
+			continue;
+
+		char* entry_path;
+		if ( asprintf(&entry_path, "%s%s%s", path, joiner, entry->d_name) < 0 )
+		{
+			error(0, errno, "asprintf: `%s%s%s'", path, joiner, entry->d_name);
+			success = false;
+			continue;
+		}
+
+		if ( !do_chmod(fd, entry->d_name, entry_path, modespec, flags, symderef) )
+			success = false;
+
+		free(entry_path);
+	}
+
+	if ( derror(dir) )
+	{
+		error(0, errno, "reading directory: `%s'", path);
+		closedir(dir);
+		return false;
+	}
+
+	closedir(dir);
+	return success;
+}
+
+static bool is_ambiguous_option(const char* str)
+{
+	if ( str[0] != '-' )
+		return false;
+	if ( str[1] == '-' )
+		return false;
+	return is_valid_modespec(str);
+}
+
+static void compact_arguments(int* argc, char*** argv)
+{
+	for ( int i = 0; i < *argc; i++ )
+	{
+		while ( i < *argc && !(*argv)[i] )
+		{
+			for ( int n = i; n < *argc; n++ )
+				(*argv)[n] = (*argv)[n+1];
+			(*argc)--;
+		}
+	}
+}
+
+static void help(FILE* fp, const char* argv0)
+{
+	fprintf(fp, "Usage: %s [OPTION]... MODE[,MODE]... FILE\n", argv0);
+	fprintf(fp, "  or:  %s [OPTION]... OCTAL-MODE FILE...\n", argv0);
+#if 0
+	fprintf(fp, "  or:  %s [OPTION]... --reference=RFILE FILE...\n", argv0);
+#endif
+}
+
+static void version(FILE* fp, const char* argv0)
+{
+	fprintf(fp, "%s (Sortix) %s\n", argv0, VERSIONSTR);
+	fprintf(fp, "License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.\n");
+	fprintf(fp, "This is free software: you are free to change and redistribute it.\n");
+	fprintf(fp, "There is NO WARRANTY, to the extent permitted by law.\n");
+}
+
+int main(int argc, char* argv[])
+{
+	int flags = 0;
+	enum symderef symderef = SYMDEREF_DEFAULT;
+
+	const char* argv0 = argv[0];
+	for ( int i = 1; i < argc; i++ )
+	{
+		const char* arg = argv[i];
+		if ( arg[0] != '-' || !arg[1] )
+			continue;
+		if ( !strcmp(arg, "--") )
+			break;
+		if ( is_ambiguous_option(arg) )
+			continue;
+		argv[i] = NULL;
+		if ( arg[1] != '-' )
+		{
+			while ( char c = *++arg ) switch ( c )
+			{
+			case 'c': flags |= FLAG_CHANGES; break;
+			case 'H': symderef = SYMDEREF_ARGUMENTS; break;
+			case 'L': symderef = SYMDEREF_ALWAYS; break;
+			case 'P': symderef = SYMDEREF_NONE; break;
+			case 'R': flags |= FLAG_RECURSIVE; break;
+			case 'v': flags |= FLAG_VERBOSE; break;
+			default:
+				fprintf(stderr, "%s: unknown option -- '%c'\n", argv0, c);
+				help(stderr, argv0);
+				exit(1);
+			}
+		}
+		else if ( !strcmp(arg, "--help") )
+			help(stdout, argv0), exit(0);
+		else if ( !strcmp(arg, "--version") )
+			version(stdout, argv0), exit(0);
+		else if ( !strcmp(arg, "--changes") )
+			flags |= FLAG_CHANGES;
+		else if ( !strcmp(arg, "--verbose") )
+			flags |= FLAG_VERBOSE;
+		else if ( !strcmp(arg, "--recursive") )
+			flags |= FLAG_RECURSIVE;
+		else
+		{
+			fprintf(stderr, "%s: unknown option: %s\n", argv0, arg);
+			help(stderr, argv0);
+			exit(1);
+		}
+	}
+
+	compact_arguments(&argc, &argv);
+
+	if ( flags & FLAG_RECURSIVE )
+	{
+		if ( symderef == SYMDEREF_DEFAULT )
+			symderef = SYMDEREF_NONE;
+	}
+	else
+	{
+		symderef = SYMDEREF_NONE;
+	}
+
+	if ( argc == 1 )
+		error(1, 0, "missing operand");
+
+	const char* modespec = argv[1];
+
+	if ( !is_valid_modespec(modespec) )
+		error(1, 0, "invalid mode: `%s'", modespec);
+
+	if ( argc == 2 )
+		error(1, 0, "missing operand after `%s'", modespec);
+
+	bool success = true;
+	for ( int i = 2; i < argc; i++ )
+	{
+		const char* arg = argv[i];
+		if ( !do_chmod(AT_FDCWD, arg, arg, modespec, flags, symderef) )
+			success = false;
+	}
+
+	return success ? 0 : 1;
+}