Patch from Ned Ludd, solar at gentoo dot org:

I had previously provided you with a patch to help complete busybox's
props suite, but have heard no word back. Sense then I've made use of as
many of busybox's native API settings as I could find and would really
love for you to include support for this. If there is something more I
need to do to get this supported added in please let me know.

include/applets.h

@@ -553,6 +553,9 @@
 #ifdef CONFIG_SYNC
 	APPLET(sync, sync_main, _BB_DIR_BIN, _BB_SUID_NEVER)
 #endif
+#ifdef CONFIG_SYSCTL
+	APPLET(sysctl, sysctl_main, _BB_DIR_SBIN, _BB_SUID_NEVER)
+#endif
 #ifdef CONFIG_SYSLOGD
 	APPLET(syslogd, syslogd_main, _BB_DIR_SBIN, _BB_SUID_NEVER)
 #endif

include/usage.h

@@ -2266,6 +2266,27 @@
   #define USAGE_IPC_LOG(a)
 #endif
 
+#ifdef CONFIG_SYSCTL
+#define sysctl_trivial_usage \
+	"[OPTIONS]... [VALUE]...\n"
+#define sysctl_full_usage
+	"sysctl - configure kernel parameters at runtime\n\n" \
+	"Options:\n" \
+	"\t-n\tUse this option to disable printing of the key name when printing values.\n" \
+	"\t-e\tUse this option to ignore errors about unknown keys.\n" \
+	"\t-w\tUse this option when you want to change a sysctl setting.\n" \
+	"\t-p\tLoad in sysctl settings from the file specified or /etc/sysctl.conf if none given.\n" \
+	"\t-a\tDisplay all values currently available.\n" \
+	"\t-A\tDisplay all values currently available in table form."
+
+#define sysctl_example_usage
+	"sysctl [-n] [-e] variable ...\n" \
+	"sysctl [-n] [-e] -w variable=value ...\n" \
+	"sysctl [-n] [-e] -a\n" \
+	"sysctl [-n] [-e] -p <file>\t(default /etc/sysctl.conf)\n" \
+	"sysctl [-n] [-e] -A\n"
+#endif
+
 #define syslogd_trivial_usage \
 	"[OPTION]..."
 #define syslogd_full_usage \

procps/Config.in

@@ -72,5 +72,11 @@ config CONFIG_UPTIME
 	  the system has been running, how many users are currently logged
 	  on, and the system load averages for the past 1, 5, and 15 minutes.
 
+config CONFIG_SYSCTL
+	bool "sysctl"
+	default n
+	help
+	  sysctl - configure kernel parameters at runtime
+
 endmenu
 

procps/Makefile.in

@@ -28,6 +28,7 @@ PROCPS-$(CONFIG_KILL)		+= kill.o
 PROCPS-$(CONFIG_PIDOF)		+= pidof.o
 PROCPS-$(CONFIG_PS)		+= ps.o
 PROCPS-$(CONFIG_RENICE)		+= renice.o
+PROCPS-$(CONFIG_SYSCTL)		+= sysctl.o
 PROCPS-$(CONFIG_TOP)		+= top.o
 PROCPS-$(CONFIG_UPTIME)		+= uptime.o
 

procps/sysctl.c

@@ -0,0 +1,372 @@
+
+/*
+ * Sysctl 1.01 - A utility to read and manipulate the sysctl parameters
+ *
+ *
+ * "Copyright 1999 George Staikos
+ * This file may be used subject to the terms and conditions of the
+ * GNU General Public License Version 2, or any later version
+ * at your option, as published by the Free Software Foundation.
+ * 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."
+ *
+ * Changelog:
+ *	v1.01:
+ *		- added -p <preload> to preload values from a file
+ *	v1.01.1
+ *		- busybox applet aware by <solar@gentoo.org>
+ * 
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include "busybox.h"
+
+/*
+ *    Function Prototypes
+ */
+static int sysctl_usage(void);
+static int sysctl_read_setting(const char *setting, int output);
+static int sysctl_write_setting(const char *setting, int output);
+static int sysctl_preload_file(const char *filename, int output);
+static int sysctl_display_all(const char *path, int output, int show_table);
+
+/*
+ *    Globals...
+ */
+static const char *PROC_PATH = "/proc/sys/";
+static const char *DEFAULT_PRELOAD = "/etc/sysctl.conf";
+
+/* error messages */
+static const char *ERR_UNKNOWN_PARAMETER = "error: Unknown parameter '%s'\n";
+static const char *ERR_MALFORMED_SETTING = "error: Malformed setting '%s'\n";
+static const char *ERR_NO_EQUALS =
+	"error: '%s' must be of the form name=value\n";
+static const char *ERR_INVALID_KEY = "error: '%s' is an unknown key\n";
+static const char *ERR_UNKNOWN_WRITING =
+	"error: unknown error %d setting key '%s'\n";
+static const char *ERR_UNKNOWN_READING =
+	"error: unknown error %d reading key '%s'\n";
+static const char *ERR_PERMISSION_DENIED =
+	"error: permission denied on key '%s'\n";
+static const char *ERR_OPENING_DIR = "error: unable to open directory '%s'\n";
+static const char *ERR_PRELOAD_FILE =
+	"error: unable to open preload file '%s'\n";
+static const char *WARN_BAD_LINE =
+	"warning: %s(%d): invalid syntax, continuing...\n";
+
+
+/*
+ *    sysctl_main()... 
+ */
+int sysctl_main(int argc, char **argv)
+{
+	int retval = 0;
+	int output = 1;
+	int write_mode = 0;
+	int switches_allowed = 1;
+
+	if (argc < 2)
+		return sysctl_usage();
+
+	argv++;
+
+	for (; argv && *argv && **argv; argv++) {
+		if (switches_allowed && **argv == '-') {	/* we have a switch */
+			switch ((*argv)[1]) {
+			case 'n':
+				output = 0;
+				break;
+			case 'w':
+				write_mode = 1;
+				switches_allowed = 0;
+				break;
+			case 'p':
+				argv++;
+				return
+					sysctl_preload_file(((argv && *argv
+										  && **argv) ? *argv :
+										 DEFAULT_PRELOAD), output);
+			case 'a':
+			case 'A':
+				switches_allowed = 0;
+				return sysctl_display_all(PROC_PATH, output,
+										  ((*argv)[1] == 'a') ? 0 : 1);
+			case 'h':
+			case '?':
+				return sysctl_usage();
+			default:
+				bb_error_msg(ERR_UNKNOWN_PARAMETER, *argv);
+				return sysctl_usage();
+			}
+		} else {
+			switches_allowed = 0;
+			if (write_mode)
+				retval = sysctl_write_setting(*argv, output);
+			else
+				sysctl_read_setting(*argv, output);
+		}
+	}
+	return retval;
+}						/* end sysctl_main() */
+
+/*
+ *     Display the sysctl_usage format
+ */
+int sysctl_usage()
+{
+	bb_show_usage();
+	return -1;
+}						/* end sysctl_usage() */
+
+
+/*
+ *     sysctl_preload_file 
+ *	preload the sysctl's from a conf file
+ *           - we parse the file and then reform it (strip out whitespace)
+ */
+int sysctl_preload_file(const char *filename, int output)
+{
+	int lineno = 0;
+	char oneline[256];
+	char buffer[256];
+	char *name, *value, *ptr;
+	FILE *fp = NULL;
+
+	if (!filename || ((fp = fopen(filename, "r")) == NULL)) {
+		bb_error_msg(ERR_PRELOAD_FILE, filename);
+		return 1;
+	}
+
+	while (fgets(oneline, sizeof(oneline) - 1, fp)) {
+		oneline[sizeof(oneline) - 1] = 0;
+		lineno++;
+		trim(oneline);
+		ptr = (char *) oneline;
+
+		if (*ptr == '#' || *ptr == ';')
+			continue;
+
+		if (bb_strlen(ptr) < 2)
+			continue;
+
+		name = strtok(ptr, "=");
+		if (!name || !*name) {
+			bb_error_msg(WARN_BAD_LINE, filename, lineno);
+			continue;
+		}
+
+		trim(name);
+
+		value = strtok(NULL, "\n\r");
+		if (!value || !*value) {
+			bb_error_msg(WARN_BAD_LINE, filename, lineno);
+			continue;
+		}
+
+		while ((*value == ' ' || *value == '\t') && *value != 0)
+			value++;
+		strncpy(buffer, name, sizeof(buffer));
+		strncat(buffer, "=", sizeof(buffer));
+		strncat(buffer, value, sizeof(buffer));
+		sysctl_write_setting(buffer, output);
+	}
+	fclose(fp);
+	return 0;
+}						/* end sysctl_preload_file() */
+
+
+/*
+ *     Write a single sysctl setting
+ */
+int sysctl_write_setting(const char *setting, int output)
+{
+	int retval = 0;
+	const char *name = setting;
+	const char *value;
+	const char *equals;
+	char *tmpname, *outname, *cptr;
+	int fd = -1;
+
+	if (!name)			/* probably dont' want to display this  err */
+		return 0;
+
+	if (!(equals = index(setting, '='))) {
+		bb_error_msg(ERR_NO_EQUALS, setting);
+		return -1;
+	}
+
+	value = equals + sizeof(char);	/* point to the value in name=value */
+
+	if (!*name || !*value || name == equals) {
+		bb_error_msg(ERR_MALFORMED_SETTING, setting);
+		return -2;
+	}
+
+	tmpname =
+		(char *) xmalloc((equals - name + 1 + bb_strlen(PROC_PATH)) *
+						 sizeof(char));
+	outname = (char *) xmalloc((equals - name + 1) * sizeof(char));
+
+	strcpy(tmpname, PROC_PATH);
+	strncat(tmpname, name, (int) (equals - name));
+	tmpname[equals - name + bb_strlen(PROC_PATH)] = 0;
+	strncpy(outname, name, (int) (equals - name));
+	outname[equals - name] = 0;
+
+	while ((cptr = strchr(tmpname, '.')) != NULL)
+		*cptr = '/';
+
+	while ((cptr = strchr(outname, '/')) != NULL)
+		*cptr = '.';
+
+	if ((fd = open(tmpname, O_WRONLY | O_CREAT | O_TRUNC, 0666)) < 0) {
+		switch (errno) {
+		case ENOENT:
+			bb_error_msg(ERR_INVALID_KEY, outname);
+			break;
+		case EACCES:
+			bb_perror_msg(ERR_PERMISSION_DENIED, outname);
+			break;
+		default:
+			bb_error_msg(ERR_UNKNOWN_WRITING, errno, outname);
+			break;
+		}
+		retval = -1;
+	} else {
+		write(fd, value, bb_strlen(value));
+		close(fd);
+		if (output) {
+			write(STDOUT_FILENO, outname, bb_strlen(outname));
+			write(STDOUT_FILENO, " = ", 3);
+		}
+		write(STDOUT_FILENO, value, bb_strlen(value));
+		write(STDOUT_FILENO, "\n", 1);
+	}
+
+	/* cleanup */
+	free(tmpname);
+	free(outname);
+	return retval;
+}						/* end sysctl_write_setting() */
+
+
+/*
+ *     Read a sysctl setting 
+ *
+ */
+int sysctl_read_setting(const char *setting, int output)
+{
+	int retval = 0;
+	char *tmpname, *outname, *cptr;
+	char inbuf[1025];
+	const char *name = setting;
+	FILE *fp;
+
+	if (!setting || !*setting)
+		bb_error_msg(ERR_INVALID_KEY, setting);
+
+	tmpname =
+		(char *) xmalloc((bb_strlen(name) + bb_strlen(PROC_PATH) + 1) *
+						 sizeof(char));
+	outname = (char *) xmalloc((bb_strlen(name) + 1) * sizeof(char));
+
+	strcpy(tmpname, PROC_PATH);
+	strcat(tmpname, name);
+	strcpy(outname, name);
+
+	while ((cptr = strchr(tmpname, '.')) != NULL)
+		*cptr = '/';
+	while ((cptr = strchr(outname, '/')) != NULL)
+		*cptr = '.';
+
+	if ((fp = fopen(tmpname, "r")) == NULL) {
+		switch (errno) {
+		case ENOENT:
+			bb_error_msg(ERR_INVALID_KEY, outname);
+			break;
+		case EACCES:
+			bb_error_msg(ERR_PERMISSION_DENIED, outname);
+			break;
+		default:
+			bb_error_msg(ERR_UNKNOWN_READING, errno, outname);
+			break;
+		}
+		retval = -1;
+	} else {
+		while (fgets(inbuf, sizeof(inbuf) - 1, fp)) {
+			if (output) {
+				write(STDOUT_FILENO, outname, bb_strlen(outname));
+				write(STDOUT_FILENO, " = ", 3);
+			}
+			write(STDOUT_FILENO, inbuf, bb_strlen(inbuf));
+		}
+		fclose(fp);
+	}
+
+	free(tmpname);
+	free(outname);
+	return retval;
+}						/* end sysctl_read_setting() */
+
+
+
+/*
+ *     Display all the sysctl settings 
+ *
+ */
+int sysctl_display_all(const char *path, int output, int show_table)
+{
+	int retval = 0;
+	int retval2;
+	DIR *dp;
+	struct dirent *de;
+	char *tmpdir;
+	struct stat ts;
+
+	if (!(dp = opendir(path))) {
+		bb_perror_msg(ERR_OPENING_DIR, path);
+		retval = -1;
+	} else {
+		readdir(dp);
+		readdir(dp);	/* skip . and .. */
+		while ((de = readdir(dp)) != NULL) {
+			tmpdir =
+				(char *) xmalloc(bb_strlen(path) + bb_strlen(de->d_name) + 2);
+			strcpy(tmpdir, path);
+			strcat(tmpdir, de->d_name);
+			if ((retval2 = stat(tmpdir, &ts)) != 0)
+				bb_perror_msg(tmpdir);
+			else {
+				if (S_ISDIR(ts.st_mode)) {
+					strcat(tmpdir, "/");
+					sysctl_display_all(tmpdir, output, show_table);
+				} else
+					retval |=
+						sysctl_read_setting(tmpdir + bb_strlen(PROC_PATH),
+											output);
+
+			}
+			free(tmpdir);
+		}				/* end while */
+		closedir(dp);
+	}
+
+	return retval;
+}						/* end sysctl_display_all() */
+
+#ifdef STANDALONE_SYSCTL
+int main(int argc, char **argv)
+{
+	return sysctl_main(argc, argv);
+}
+#endif