diff --git a/apps/chown.cpp b/apps/chown.cpp
index 16416cd3..b856c0dc 100644
--- a/apps/chown.cpp
+++ b/apps/chown.cpp
@@ -1,3 +1,4 @@
+#include <grp.h>
 #include <luna/String.h>
 #include <os/ArgumentParser.h>
 #include <pwd.h>
@@ -31,8 +32,14 @@ Result<int> luna_main(int argc, char** argv)
             if (rc.has_value()) { gid = (u32)rc.value(); }
             else
             {
-                fprintf(stderr, "FIXME: read entry from group file to determine GID for group %s\n", group.chars());
-                return 1;
+                struct group* grp = getgrnam(group.chars());
+                if (!grp)
+                {
+                    fprintf(stderr, "%s: unknown group %s!\n", argv[0], group.chars());
+                    return 1;
+                }
+
+                gid = grp->gr_gid;
             }
         }
     }
diff --git a/initrd/etc/group b/initrd/etc/group
new file mode 100644
index 00000000..59582096
--- /dev/null
+++ b/initrd/etc/group
@@ -0,0 +1,3 @@
+root:!:0:
+users:!:1:
+selene:!:1000:
diff --git a/libc/include/grp.h b/libc/include/grp.h
new file mode 100644
index 00000000..e00eca0e
--- /dev/null
+++ b/libc/include/grp.h
@@ -0,0 +1,40 @@
+/* grp.h: Group file parsing. */
+
+#ifndef _GRP_H
+#define _GRP_H
+
+#include <sys/types.h>
+
+struct group
+{
+    char* gr_name;
+    char* gr_passwd;
+    gid_t gr_gid;
+    char** gr_mem;
+};
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    /* Read the next entry from the group file. */
+    struct group* getgrent(void);
+
+    /* Find the entry with a matching group name in the group file. */
+    struct group* getgrnam(const char* name);
+
+    /* Find the entry with a matching group ID in the group file. */
+    struct group* getgrgid(gid_t gid);
+
+    /* Rewind the group file. */
+    void setgrent(void);
+
+    /* End group file parsing. */
+    void endgrent(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/libc/src/grp.cpp b/libc/src/grp.cpp
new file mode 100644
index 00000000..37efaa3e
--- /dev/null
+++ b/libc/src/grp.cpp
@@ -0,0 +1,128 @@
+#include <errno.h>
+#include <grp.h>
+#include <luna/Vector.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static struct group grp;
+static FILE* f { nullptr };
+static char buf[4096];
+
+static Vector<char*> g_members;
+
+extern char* _strtok_once(char* str, const char* delim);
+
+extern "C"
+{
+    static Result<struct group*> try_getgrent()
+    {
+        if (!f)
+        {
+            f = fopen("/etc/group", "r");
+            if (!f) return nullptr;
+        }
+
+        while (true)
+        {
+            char* rc = fgets(buf, sizeof(buf), f);
+            if (!rc) return nullptr;
+
+            char* name = _strtok_once(rc, ":\n");
+            if (!name) continue;
+
+            char* passwd = _strtok_once(nullptr, ":\n");
+            if (!passwd) continue;
+
+            char* gid = _strtok_once(nullptr, ":\n");
+            if (!gid) continue;
+
+            char* members = _strtok_once(nullptr, ":\n");
+            if (!members) continue;
+
+            g_members.clear();
+
+            char* member = strtok(members, ",");
+            TRY(g_members.try_append(member));
+
+            if (member)
+            {
+                while (true)
+                {
+                    member = strtok(nullptr, ",");
+                    TRY(g_members.try_append(member));
+                    if (!member) break;
+                }
+            }
+
+            grp.gr_name = name;
+            grp.gr_passwd = passwd;
+            grp.gr_gid = (gid_t)strtoul(gid, NULL, 10);
+            grp.gr_mem = g_members.data();
+
+            return &grp;
+        }
+    }
+
+    struct group* getgrent()
+    {
+        auto rc = try_getgrent();
+        if (rc.has_error())
+        {
+            errno = rc.error();
+            return nullptr;
+        }
+        return rc.value();
+    }
+
+    struct group* getgrnam(const char* name)
+    {
+        setgrent();
+
+        struct group* entry;
+
+        while ((entry = getgrent()))
+        {
+            if (!strcmp(entry->gr_name, name))
+            {
+                endgrent();
+                return entry;
+            }
+        }
+
+        endgrent();
+        return entry;
+    }
+
+    struct group* getgrgid(gid_t gid)
+    {
+        setgrent();
+
+        struct group* entry;
+
+        while ((entry = getgrent()))
+        {
+            if (entry->gr_gid == gid)
+            {
+                endgrent();
+                return entry;
+            }
+        }
+
+        endgrent();
+        return entry;
+    }
+
+    void setgrent()
+    {
+        if (f) rewind(f);
+    }
+
+    void endgrent()
+    {
+        if (f)
+        {
+            fclose(f);
+            f = nullptr;
+        }
+    }
+}
diff --git a/libc/src/pwd.cpp b/libc/src/pwd.cpp
index 33c1eaf5..80a0bae7 100644
--- a/libc/src/pwd.cpp
+++ b/libc/src/pwd.cpp
@@ -11,7 +11,7 @@ static char buf[4096];
 // Example:
 // strtok("hello:world::!:", ":") -> "hello", "world", "!"
 // _strtok_once("hello:world::!:", ":") -> "hello", "world", "", "!"
-static char* _strtok_once(char* str, const char* delim)
+char* _strtok_once(char* str, const char* delim)
 {
     static char* s = nullptr;
     if (str) s = str;