diff --git a/Makefile b/Makefile
index 9bba950..eaec230 100644
--- a/Makefile
+++ b/Makefile
@@ -3,11 +3,16 @@ include config.mk
 .POSIX:
 .SUFFIXES: .c .o
 
-HDR = arg.h ubase.h util.h
+HDR = arg.h grabmntinfo.h proc.h util.h
 LIB = \
+	util/agetcwd.o      \
+	util/apathmax.o     \
 	util/eprintf.o      \
 	util/estrtol.o      \
-	util/grabmntinfo.o
+	util/grabmntinfo.o  \
+	util/proc.o         \
+	util/recurse.o      \
+	util/tty.o
 
 SRC = \
 	df.c                \
@@ -18,6 +23,7 @@ SRC = \
 	mkswap.c            \
 	mount.c             \
 	pivot_root.c        \
+	ps.c                \
 	reboot.c            \
 	rmmod.c             \
 	stat.c              \
diff --git a/proc.h b/proc.h
new file mode 100644
index 0000000..6785ade
--- /dev/null
+++ b/proc.h
@@ -0,0 +1,32 @@
+/* See LICENSE file for copyright and license details. */
+struct procstat {
+	int pid;
+	char comm[PATH_MAX + 2]; /* + 2 for '(' and ')' */
+	unsigned char state;
+	int ppid;
+	int pgrp;
+	int sid;
+	int tty_nr;
+	int tpgid;
+	unsigned flags;
+	unsigned long minflt;
+	unsigned long cminflt;
+	unsigned long majflt;
+	unsigned long cmajflt;
+	unsigned long utime;
+	unsigned long stime;
+	long cutime;
+	long cstime;
+	long priority;
+	long nice;
+	long num_threads;
+	long itrealvalue;
+	unsigned long long starttime;
+	unsigned long vsize;
+	long rss;
+	long rsslim;
+};
+
+int parsestat(pid_t pid, struct procstat *ps);
+int proceuid(pid_t pid, uid_t *euid);
+int validps(const char *path);
diff --git a/ps.c b/ps.c
new file mode 100644
index 0000000..652fded
--- /dev/null
+++ b/ps.c
@@ -0,0 +1,116 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include "proc.h"
+#include "util.h"
+
+static void usage(void);
+static void psout(struct procstat *ps);
+static void psr(const char *path);
+
+enum {
+	PS_aflag = 1 << 0,
+	PS_Aflag = 1 << 1,
+	PS_dflag = 1 << 2
+};
+
+static int flags;
+
+int
+main(int argc, char *argv[])
+{
+	ARGBEGIN {
+	case 'a':
+		flags |= PS_aflag;
+		break;
+	case 'A':
+		flags |= PS_Aflag;
+		break;
+	case 'd':
+		flags |= PS_dflag;
+		break;
+	case 'e':
+		flags |= PS_Aflag;
+		break;
+	case 'f':
+		eprintf("not implemented\n");
+	default:
+		usage();
+	} ARGEND;
+
+	printf("  PID TTY          TIME CMD\n");
+	recurse("/proc", psr);
+
+	return 0;
+}
+
+static void
+usage(void)
+{
+	eprintf("usage: [-aAdef] %s\n", argv0);
+}
+
+static void
+psout(struct procstat *ps)
+{
+	char *ttystr, *myttystr;
+	int tty_maj, tty_min;
+	uid_t myeuid, peuid;
+	unsigned sut;
+
+	/* Ignore session leaders */
+	if (flags & PS_dflag)
+		if (ps->pid == ps->sid)
+			return;
+
+	sut = (ps->stime + ps->utime) / 100;
+
+	devtotty(ps->tty_nr, &tty_maj, &tty_min);
+	ttystr = ttytostr(tty_maj, tty_min);
+	/* Only print processes that are associated with
+	 * a terminal */
+	if (ttystr[0] == '?' && (flags & PS_aflag)) {
+		free(ttystr);
+		return;
+	}
+
+	if (!flags) {
+		myttystr = ttyname(STDIN_FILENO);
+		if (myttystr) {
+			if (strcmp(myttystr + strlen("/dev/"), ttystr)) {
+				free(ttystr);
+				return;
+			}
+		} else {
+			ttystr[0] = '?';
+			ttystr[1] = '\0';
+		}
+		proceuid(ps->pid, &peuid);
+		myeuid = geteuid();
+		if (myeuid != peuid) {
+			free(ttystr);
+			return;
+		}
+	}
+
+	printf("%5d %-6s   %02u:%02u:%02u %s\n", ps->pid, ttystr,
+	       sut / 3600, (sut % 3600) / 60, sut % 60, ps->comm);
+	free(ttystr);
+}
+
+static void
+psr(const char *path)
+{
+	struct procstat ps;
+	pid_t pid;
+
+	if (!validps(path))
+		return;
+	pid = estrtol(path, 10);
+	parsestat(pid, &ps);
+	psout(&ps);
+}
diff --git a/util.h b/util.h
index d2f9399..e686733 100644
--- a/util.h
+++ b/util.h
@@ -6,6 +6,11 @@
 
 extern char *argv0;
 
-void eprintf(const char *, ...);
+char *agetcwd(void);
+void apathmax(char **, long *);
+void devtotty(int dev, int *tty_maj, int *tty_min);
 void enprintf(int, const char *, ...);
+void eprintf(const char *, ...);
 long estrtol(const char *, int);
+void recurse(const char *, void (*)(const char *));
+char *ttytostr(int tty_maj, int tty_min);
diff --git a/util/agetcwd.c b/util/agetcwd.c
new file mode 100644
index 0000000..a672bcf
--- /dev/null
+++ b/util/agetcwd.c
@@ -0,0 +1,18 @@
+/* See LICENSE file for copyright and license details. */
+#include <unistd.h>
+
+#include "../util.h"
+
+char *
+agetcwd(void)
+{
+	char *buf;
+	long size;
+
+	apathmax(&buf, &size);
+	if(!getcwd(buf, size))
+		eprintf("getcwd:");
+
+	return buf;
+}
+
diff --git a/util/apathmax.c b/util/apathmax.c
new file mode 100644
index 0000000..5dc831f
--- /dev/null
+++ b/util/apathmax.c
@@ -0,0 +1,25 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "../util.h"
+
+void
+apathmax(char **p, long *size)
+{
+	errno = 0;
+
+	if((*size = pathconf("/", _PC_PATH_MAX)) == -1) {
+		if(errno == 0) {
+			*size = BUFSIZ;
+		} else {
+			eprintf("pathconf:");
+		}
+	}
+
+	if(!(*p = malloc(*size)))
+		eprintf("malloc:");
+}
+
diff --git a/util/proc.c b/util/proc.c
new file mode 100644
index 0000000..ac6b991
--- /dev/null
+++ b/util/proc.c
@@ -0,0 +1,73 @@
+/* See LICENSE file for copyright and license details. */
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include "../proc.h"
+#include "../util.h"
+
+int
+proceuid(pid_t pid, uid_t *euid)
+{
+	FILE *fp;
+	char buf[BUFSIZ], *p;
+	char path[PATH_MAX];
+	uid_t procuid, proceuid;
+
+	snprintf(path, sizeof(path), "/proc/%d/status", pid);
+	if (!(fp = fopen(path, "r")))
+		eprintf("%s fopen:", path);
+	while (fgets(buf, sizeof(buf), fp)) {
+		if (!strncmp(buf, "Uid:", 4)) {
+			p = buf + strlen("Uid:");
+			sscanf(p, "%u %u", &procuid, &proceuid);
+			*euid = proceuid;
+			fclose(fp);
+			return 0;
+		}
+	}
+	fclose(fp);
+	return -1;
+}
+
+int
+parsestat(pid_t pid, struct procstat *ps)
+{
+	char path[PATH_MAX];
+	FILE *fp;
+
+	snprintf(path, sizeof(path), "/proc/%d/stat", pid);
+	if (!(fp = fopen(path, "r")))
+		eprintf("fopen %s:", path);
+	fscanf(fp, "%d %s %c %d %d %d %d %d %u %lu %lu %lu %lu %lu %lu",
+	       &ps->pid, ps->comm,
+	       &ps->state, &ps->ppid, &ps->pgrp,
+	       &ps->sid, &ps->tty_nr, &ps->tpgid, &ps->flags,
+	       &ps->minflt, &ps->cminflt, &ps->majflt, &ps->cmajflt,
+	       &ps->utime, &ps->stime);
+	fscanf(fp, "%ld %ld %ld %ld %ld %ld %lld %lu %ld %ld",
+	       &ps->cutime, &ps->cstime, &ps->priority, &ps->nice,
+	       &ps->num_threads, &ps->itrealvalue, &ps->starttime,
+	       &ps->vsize, &ps->rss, &ps->rsslim);
+	/* Filter out '(' and ')' from comm */
+	ps->comm[strlen(ps->comm) - 1] = '\0';
+	memmove(ps->comm, ps->comm + 1, strlen(ps->comm));
+	fclose(fp);
+	return 0;
+}
+
+int
+validps(const char *path)
+{
+	char *end;
+
+	errno = 0;
+	strtol(path, &end, 10);
+	if (*end != '\0')
+		return 0;
+	if (errno != 0)
+		return 0;
+	return 1;
+}
diff --git a/util/recurse.c b/util/recurse.c
new file mode 100644
index 0000000..b3d1f8c
--- /dev/null
+++ b/util/recurse.c
@@ -0,0 +1,40 @@
+/* See LICENSE file for copyright and license details. */
+#include <dirent.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+#include "../util.h"
+
+void
+recurse(const char *path, void (*fn)(const char *))
+{
+	char *cwd;
+	struct dirent *d;
+	struct stat st;
+	DIR *dp;
+
+	if(lstat(path, &st) == -1 || !S_ISDIR(st.st_mode)) {
+		return;
+	} else if(!(dp = opendir(path))) {
+		eprintf("opendir %s:", path);
+	}
+
+	cwd = agetcwd();
+	if(chdir(path) == -1)
+		eprintf("chdir %s:", path);
+
+	while((d = readdir(dp))) {
+		if(strcmp(d->d_name, ".") && strcmp(d->d_name, ".."))
+			fn(d->d_name);
+	}
+
+	closedir(dp);
+	if(chdir(cwd) == -1)
+		eprintf("chdir %s:", cwd);
+
+	free(cwd);
+}
+
diff --git a/util/tty.c b/util/tty.c
new file mode 100644
index 0000000..4b5e518
--- /dev/null
+++ b/util/tty.c
@@ -0,0 +1,39 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "../util.h"
+
+void
+devtotty(int dev, int *tty_maj, int *tty_min)
+{
+	*tty_maj = (dev >> 8) & 0xfff;
+	*tty_min = (dev & 0xff) | ((dev >> 12) & 0xfff00);
+}
+
+char *
+ttytostr(int tty_maj, int tty_min)
+{
+	const char *pts = "pts/";
+	const char *tty = "tty/";
+	char *ttystr;
+	size_t len;
+
+	/* Up to 10k ttys */
+	len = strlen(pts) + 4 + 1;
+	ttystr = malloc(len);
+	if (!ttystr)
+		eprintf("malloc:");
+	switch (tty_maj) {
+	case 136:
+		snprintf(ttystr, len, "%s%d", pts, tty_min);
+		break;
+	case 4:
+		snprintf(ttystr, len, "%s%d", tty, tty_min);
+	default:
+		ttystr[0] = '?';
+		ttystr[1] = '\0';
+		break;
+	}
+	return ttystr;
+}