diff --git a/lib/PackedUser.zig b/lib/PackedUser.zig
index 27603b7..2181480 100644
--- a/lib/PackedUser.zig
+++ b/lib/PackedUser.zig
@@ -237,23 +237,6 @@ const test_shell_reader = shellImport.ShellReader{
     .index = &[_]u16{ 0, 9, 17 },
 };
 
-const max_user = User{
-    .uid = 0,
-    .gid = math.maxInt(u32),
-    .name = "Name" ** 8,
-    .gecos = "realname" ** 255 ++ "realnam",
-    .home = "Home" ** 16,
-    .shell = "She.LllL" ** 32,
-};
-
-test "max_user and max_str_len are consistent" {
-    const total_len = max_user.name.len +
-        max_user.gecos.len +
-        max_user.home.len +
-        max_user.shell.len;
-    try testing.expectEqual(total_len, max_str_len);
-}
-
 test "pack max_user" {
     var arr = ArrayList(u8).init(testing.allocator);
     defer arr.deinit();
@@ -261,7 +244,7 @@ test "pack max_user" {
     var idx_noop = StringHashMap(u8).init(testing.allocator);
     defer idx_noop.deinit();
 
-    try packTo(&arr, max_user, 0, idx_noop);
+    try packTo(&arr, User.max_user, 0, idx_noop);
 }
 
 test "construct PackedUser section" {
@@ -282,7 +265,7 @@ test "construct PackedUser section" {
         .gecos = "Service Account",
         .home = "/home/service1",
         .shell = "/usr/bin/nologin",
-    }, max_user, User{
+    }, User.max_user, User{
         .uid = 1002,
         .gid = 1002,
         .name = "svc-bar",
diff --git a/lib/User.zig b/lib/User.zig
index 4152ab6..c290fb2 100644
--- a/lib/User.zig
+++ b/lib/User.zig
@@ -1,10 +1,14 @@
 const std = @import("std");
 const mem = std.mem;
+const fmt = std.fmt;
+const maxInt = std.math.maxInt;
 const Allocator = mem.Allocator;
 const ArrayList = std.ArrayList;
-const maxInt = std.math.maxInt;
+const BoundedArray = std.BoundedArray;
 
 const User = @This();
+const PackedUser = @import("PackedUser.zig");
+const validate = @import("validate.zig");
 
 uid: u32,
 gid: u32,
@@ -37,6 +41,61 @@ pub fn clone(
     };
 }
 
+const line_fmt = "{s}:x:{d}:{d}:{s}:{s}:{s}\n";
+
+const max_line_len = fmt.count(line_fmt, .{
+    max_user.uid,
+    max_user.gid,
+    max_user.gecos,
+    max_user.home,
+    max_user.shell,
+});
+
+// toPasswdLine formats the user in /etc/passwd format, including the EOL
+fn toLine(self: *const User) BoundedArray(u8, max_line_len) {
+    var result = BoundedArray(u8, max_line_len);
+    fmt.bufPrint(result.slice(), line_fmt, .{
+        self.uid,
+        self.gid,
+        self.gecos,
+        self.home,
+        self.shell,
+    });
+    return result;
+}
+
+// fromLine accepts a line of /etc/passwd (with or without the EOL) and makes a
+// User.
+fn fromLine(allocator: Allocator, line: []const u8) error{ InvalidRecord, OutOfMemory }!User {
+    var it = mem.split(u8, line, ":");
+    const uids = it.next() orelse return error.InvalidRecord;
+    const gids = it.next() orelse return error.InvalidRecord;
+    const name = it.next() orelse return error.InvalidRecord;
+    const gecos = it.next() orelse return error.InvalidRecord;
+    const home = it.next() orelse return error.InvalidRecord;
+    const shell = it.next() orelse return error.InvalidRecord;
+    // the line must be exhaustive.
+    if (it.next() != null) return error.InvalidRecord;
+
+    const uid = fmt.parseInt(u32, uids) orelse return error.InvalidRecord;
+    const gid = fmt.parseInt(u32, gids) orelse return error.InvalidRecord;
+
+    try validate.utf8(name);
+    try validate.utf8(gecos);
+    try validate.utf8(home);
+    try validate.utf8(shell);
+
+    const user = User{
+        .uid = uid,
+        .gid = gid,
+        .name = name,
+        .gecos = gecos,
+        .home = home,
+        .shell = shell,
+    };
+    return try user.clone(allocator);
+}
+
 fn strlen(self: *const User) usize {
     return self.name.len +
         self.gecos.len +
@@ -63,6 +122,23 @@ pub fn fromReader(allocator: Allocator, reader: anytype) ![]User {
 
 const testing = std.testing;
 
+pub const max_user = User{
+    .uid = maxInt(u32),
+    .gid = maxInt(u32),
+    .name = "Name" ** 8,
+    .gecos = "realname" ** 255 ++ "realnam",
+    .home = "Home" ** 16,
+    .shell = "She.LllL" ** 32,
+};
+
+test "max_user and max_str_len are consistent" {
+    const total_len = max_user.name.len +
+        max_user.gecos.len +
+        max_user.home.len +
+        max_user.shell.len;
+    try testing.expectEqual(total_len, PackedUser.max_str_len);
+}
+
 test "User.clone" {
     var allocator = testing.allocator;
     const user = User{