From 81d0e1776d45d1b9c83643ecb5cb5e68ada866d9 Mon Sep 17 00:00:00 2001
From: Pierre Warnier <pierre@warnier.net>
Date: Tue, 24 Mar 2026 13:05:40 +0100
Subject: [PATCH] docs/fixes: man pages, benchmarks, BSD research, Copilot
 findings
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Fixes #56 — 14 man pages in docs/man/ (markdown format).
Fixes #67 — 8 Copilot findings fixed:
  - useradd: proper date validation (Feb 31 rejected)
  - userdel/usermod: --root wired to SysRoot
  - usermod: --expiredate validates input
  - usermod: --login validates name + updates shadow/group
  - userdel: -f separated from -r behavior
  - useradd: home dir resolved through SysRoot
  - skel: preserves directory permissions
Fixes #69 — benchmark script (benches/benchmark.sh)
Fixes #70 — FreeBSD/NetBSD reference (docs/FREEBSD-NETBSD-REFERENCE.md)

456 tests, zero clippy warnings.
---
 benches/benchmark.sh             | 270 +++++++++++++++++++++++++++++++
 docs/FREEBSD-NETBSD-REFERENCE.md |  63 ++++++++
 docs/man/chage.1.md              |  70 ++++++++
 docs/man/chfn.1.md               |  60 +++++++
 docs/man/chpasswd.8.md           |  56 +++++++
 docs/man/chsh.1.md               |  50 ++++++
 docs/man/groupadd.8.md           |  80 +++++++++
 docs/man/groupdel.8.md           |  54 +++++++
 docs/man/groupmod.8.md           |  70 ++++++++
 docs/man/grpck.8.md              |  68 ++++++++
 docs/man/newgrp.1.md             |  50 ++++++
 docs/man/passwd.1.md             | 104 ++++++++++++
 docs/man/pwck.8.md               |  74 +++++++++
 docs/man/useradd.8.md            | 136 ++++++++++++++++
 docs/man/userdel.8.md            |  67 ++++++++
 docs/man/usermod.8.md            |  93 +++++++++++
 src/shadow-core/src/skel.rs      |   6 +
 src/uu/useradd/src/useradd.rs    | 111 +++++++++++--
 src/uu/userdel/src/userdel.rs    |   7 +-
 src/uu/usermod/src/usermod.rs    |  58 ++++++-
 20 files changed, 1525 insertions(+), 22 deletions(-)
 create mode 100755 benches/benchmark.sh
 create mode 100644 docs/FREEBSD-NETBSD-REFERENCE.md
 create mode 100644 docs/man/chage.1.md
 create mode 100644 docs/man/chfn.1.md
 create mode 100644 docs/man/chpasswd.8.md
 create mode 100644 docs/man/chsh.1.md
 create mode 100644 docs/man/groupadd.8.md
 create mode 100644 docs/man/groupdel.8.md
 create mode 100644 docs/man/groupmod.8.md
 create mode 100644 docs/man/grpck.8.md
 create mode 100644 docs/man/newgrp.1.md
 create mode 100644 docs/man/passwd.1.md
 create mode 100644 docs/man/pwck.8.md
 create mode 100644 docs/man/useradd.8.md
 create mode 100644 docs/man/userdel.8.md
 create mode 100644 docs/man/usermod.8.md

diff --git a/benches/benchmark.sh b/benches/benchmark.sh
new file mode 100755
index 0000000..9f8a625
--- /dev/null
+++ b/benches/benchmark.sh
@@ -0,0 +1,270 @@
+#!/usr/bin/env bash
+# spell-checker:ignore timeformat tempdir ldd passwd pwck
+#
+# Benchmark script for shadow-rs vs GNU shadow-utils.
+#
+# Compares performance, binary size, and shared library dependencies
+# between shadow-rs (Rust) and GNU shadow-utils (C) implementations.
+#
+# Usage:
+#   docker compose run --rm debian bash benches/benchmark.sh
+#
+# Requirements:
+#   - Must run inside Docker (needs both GNU shadow-utils and shadow-rs)
+#   - Must run as root (passwd -S and pwck require root or shadow access)
+#
+# The script builds shadow-rs in release mode, locates GNU shadow-utils
+# binaries, and runs comparative benchmarks.
+
+set -euo pipefail
+
+# ---------------------------------------------------------------------------
+# Configuration
+# ---------------------------------------------------------------------------
+
+PASSWD_STATUS_ITERS=1000
+PWCK_ITERS=100
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+log()  { printf '\033[1;34m==> %s\033[0m\n' "$*"; }
+warn() { printf '\033[1;33mWARN: %s\033[0m\n' "$*"; }
+err()  { printf '\033[1;31mERROR: %s\033[0m\n' "$*"; exit 1; }
+
+# Print a separator line.
+separator() { printf '%.0s-' {1..72}; printf '\n'; }
+
+# Format bytes as human-readable.
+human_size() {
+    local bytes=$1
+    if [ "$bytes" -ge 1048576 ]; then
+        printf '%.1f MiB' "$(echo "$bytes / 1048576" | bc -l)"
+    elif [ "$bytes" -ge 1024 ]; then
+        printf '%.1f KiB' "$(echo "$bytes / 1024" | bc -l)"
+    else
+        printf '%d B' "$bytes"
+    fi
+}
+
+# Time a command N times, report wall-clock total in seconds.
+# Usage: bench_command <label> <iterations> <command...>
+bench_command() {
+    local label=$1
+    local iters=$2
+    shift 2
+
+    log "Benchmarking: $label ($iters iterations)"
+
+    local start end elapsed
+    start=$(date +%s%N)
+    for ((i = 0; i < iters; i++)); do
+        "$@" >/dev/null 2>&1 || true
+    done
+    end=$(date +%s%N)
+
+    elapsed=$(echo "scale=3; ($end - $start) / 1000000000" | bc)
+    local per_iter
+    per_iter=$(echo "scale=6; $elapsed / $iters" | bc)
+
+    printf '  %-30s  total: %8ss  per-iter: %ss\n' "$label" "$elapsed" "$per_iter"
+    echo "$elapsed"
+}
+
+# ---------------------------------------------------------------------------
+# Locate binaries
+# ---------------------------------------------------------------------------
+
+find_gnu_binary() {
+    local name=$1
+    # GNU shadow-utils binaries are typically in /usr/sbin or /usr/bin.
+    for path in /usr/sbin/"$name" /usr/bin/"$name" /sbin/"$name" /bin/"$name"; do
+        if [ -x "$path" ]; then
+            # Make sure it is NOT our shadow-rs binary (check for ELF or "shadow-rs").
+            if ! file "$path" 2>/dev/null | grep -q 'statically linked\|shadow-rs'; then
+                echo "$path"
+                return 0
+            fi
+        fi
+    done
+    return 1
+}
+
+# ---------------------------------------------------------------------------
+# Build shadow-rs
+# ---------------------------------------------------------------------------
+
+log "Building shadow-rs in release mode..."
+cargo build --release --quiet 2>&1
+
+SHADOW_RS_DIR="$(cargo metadata --format-version=1 --no-deps 2>/dev/null | \
+    python3 -c 'import sys,json; print(json.load(sys.stdin)["target_directory"])' 2>/dev/null || \
+    echo "target")/release"
+
+# The multicall binary.
+SHADOW_RS_BIN="$SHADOW_RS_DIR/shadow-rs"
+
+if [ ! -x "$SHADOW_RS_BIN" ]; then
+    # Try individual binaries.
+    SHADOW_RS_BIN=""
+fi
+
+# Individual tool binaries (built by cargo as separate bins).
+RS_PASSWD="$SHADOW_RS_DIR/passwd"
+RS_PWCK="$SHADOW_RS_DIR/pwck"
+
+# Fall back to the multicall binary if individual bins are not found.
+if [ ! -x "$RS_PASSWD" ] && [ -x "$SHADOW_RS_DIR/shadow-rs" ]; then
+    RS_PASSWD="$SHADOW_RS_DIR/shadow-rs"
+fi
+if [ ! -x "$RS_PWCK" ] && [ -x "$SHADOW_RS_DIR/shadow-rs" ]; then
+    RS_PWCK="$SHADOW_RS_DIR/shadow-rs"
+fi
+
+# Locate GNU binaries.
+GNU_PASSWD=$(find_gnu_binary passwd) || GNU_PASSWD=""
+GNU_PWCK=$(find_gnu_binary pwck) || GNU_PWCK=""
+
+separator
+log "Binary locations:"
+printf '  %-20s %s\n' "shadow-rs passwd:" "${RS_PASSWD:-NOT FOUND}"
+printf '  %-20s %s\n' "shadow-rs pwck:" "${RS_PWCK:-NOT FOUND}"
+printf '  %-20s %s\n' "GNU passwd:" "${GNU_PASSWD:-NOT FOUND}"
+printf '  %-20s %s\n' "GNU pwck:" "${GNU_PWCK:-NOT FOUND}"
+separator
+
+# ---------------------------------------------------------------------------
+# Binary size comparison
+# ---------------------------------------------------------------------------
+
+log "Binary size comparison"
+printf '\n'
+printf '  %-35s %12s\n' "Binary" "Size"
+separator
+
+report_size() {
+    local label=$1
+    local path=$2
+    if [ -x "$path" ]; then
+        local size
+        size=$(stat --format='%s' "$path" 2>/dev/null || stat -f '%z' "$path" 2>/dev/null || echo 0)
+        printf '  %-35s %12s (%d bytes)\n' "$label" "$(human_size "$size")" "$size"
+    else
+        printf '  %-35s %12s\n' "$label" "N/A"
+    fi
+}
+
+report_size "shadow-rs multicall" "$SHADOW_RS_DIR/shadow-rs"
+report_size "shadow-rs passwd" "$RS_PASSWD"
+report_size "shadow-rs pwck" "$RS_PWCK"
+report_size "GNU passwd" "$GNU_PASSWD"
+report_size "GNU pwck" "$GNU_PWCK"
+printf '\n'
+
+# ---------------------------------------------------------------------------
+# Shared library dependencies
+# ---------------------------------------------------------------------------
+
+log "Shared library dependencies"
+printf '\n'
+
+report_deps() {
+    local label=$1
+    local path=$2
+    if [ -x "$path" ] && command -v ldd >/dev/null 2>&1; then
+        local count
+        count=$(ldd "$path" 2>/dev/null | grep -c '=>' || echo 0)
+        printf '  %-35s %d shared libraries\n' "$label" "$count"
+        ldd "$path" 2>/dev/null | sed 's/^/      /'
+    elif [ -x "$path" ]; then
+        printf '  %-35s (ldd not available)\n' "$label"
+    else
+        printf '  %-35s N/A\n' "$label"
+    fi
+    printf '\n'
+}
+
+report_deps "shadow-rs passwd" "$RS_PASSWD"
+report_deps "GNU passwd" "$GNU_PASSWD"
+separator
+
+# ---------------------------------------------------------------------------
+# Performance benchmarks
+# ---------------------------------------------------------------------------
+
+log "Performance benchmarks"
+printf '\n'
+printf '  Test: passwd -S root (%d iterations)\n' "$PASSWD_STATUS_ITERS"
+printf '  Test: pwck -r        (%d iterations)\n' "$PWCK_ITERS"
+printf '\n'
+separator
+
+# -- passwd -S root --
+
+rs_passwd_time=""
+gnu_passwd_time=""
+
+if [ -x "$RS_PASSWD" ]; then
+    rs_passwd_time=$(bench_command "shadow-rs: passwd -S root" "$PASSWD_STATUS_ITERS" "$RS_PASSWD" -S root)
+fi
+
+if [ -x "$GNU_PASSWD" ]; then
+    gnu_passwd_time=$(bench_command "GNU: passwd -S root" "$PASSWD_STATUS_ITERS" "$GNU_PASSWD" -S root)
+fi
+
+printf '\n'
+
+# -- pwck -r --
+
+rs_pwck_time=""
+gnu_pwck_time=""
+
+if [ -x "$RS_PWCK" ]; then
+    rs_pwck_time=$(bench_command "shadow-rs: pwck -r" "$PWCK_ITERS" "$RS_PWCK" -r)
+fi
+
+if [ -x "$GNU_PWCK" ]; then
+    gnu_pwck_time=$(bench_command "GNU: pwck -r" "$PWCK_ITERS" "$GNU_PWCK" -r)
+fi
+
+printf '\n'
+
+# ---------------------------------------------------------------------------
+# Summary table
+# ---------------------------------------------------------------------------
+
+separator
+log "SUMMARY"
+printf '\n'
+printf '  %-30s %12s %12s %12s\n' "Benchmark" "shadow-rs" "GNU" "Ratio"
+separator
+
+compute_ratio() {
+    local rs=$1
+    local gnu=$2
+    if [ -n "$rs" ] && [ -n "$gnu" ] && [ "$(echo "$gnu > 0" | bc)" -eq 1 ]; then
+        printf '%.2fx' "$(echo "$rs / $gnu" | bc -l)"
+    else
+        echo "N/A"
+    fi
+}
+
+ratio_passwd=$(compute_ratio "${rs_passwd_time:-}" "${gnu_passwd_time:-}")
+ratio_pwck=$(compute_ratio "${rs_pwck_time:-}" "${gnu_pwck_time:-}")
+
+printf '  %-30s %11ss %11ss %12s\n' \
+    "passwd -S root (${PASSWD_STATUS_ITERS}x)" \
+    "${rs_passwd_time:-N/A}" \
+    "${gnu_passwd_time:-N/A}" \
+    "$ratio_passwd"
+
+printf '  %-30s %11ss %11ss %12s\n' \
+    "pwck -r (${PWCK_ITERS}x)" \
+    "${rs_pwck_time:-N/A}" \
+    "${gnu_pwck_time:-N/A}" \
+    "$ratio_pwck"
+
+printf '\n'
+separator
+log "Benchmark complete."
diff --git a/docs/FREEBSD-NETBSD-REFERENCE.md b/docs/FREEBSD-NETBSD-REFERENCE.md
new file mode 100644
index 0000000..167e2e9
--- /dev/null
+++ b/docs/FREEBSD-NETBSD-REFERENCE.md
@@ -0,0 +1,63 @@
+# FreeBSD/NetBSD Security Reference for shadow-rs
+
+Analysis of FreeBSD's `pw` and NetBSD's user management implementations.
+Both BSD-2-Clause licensed — safe to reference.
+
+## FreeBSD `pw` Patterns
+
+### What FreeBSD Does Differently
+
+| Pattern | FreeBSD | shadow-rs | Action |
+|---------|---------|-----------|--------|
+| Username allows trailing `$` | Yes (Samba compat) | No | Consider adding for Samba/AD |
+| Salt generation | `arc4random_uniform()` | PAM handles | N/A (PAM delegates hashing) |
+| Password fd input (`-h FD`) | Yes | No | Low priority — niche use case |
+| Password buffers not zeroed | Vulnerable | Fixed (zeroize) | We're ahead |
+| No mlock() on passwords | Vulnerable | Not implemented | Future work |
+| Selective config override | Sentinel values (-1) | Login.defs defaults | Already implemented |
+
+### Key Takeaway
+
+FreeBSD's `pw` is less hardened than OpenBSD's `passwd` — no explicit memory
+zeroing, no mlock, no pledge/unveil equivalent. Our implementation with
+`zeroize`, core dump suppression, and environment sanitization is already
+ahead of FreeBSD's security posture.
+
+### Patterns Worth Adopting
+
+1. **Samba-compatible usernames**: Allow trailing `$` in usernames for
+   Active Directory machine accounts. This is a common real-world need.
+
+2. **Password input via fd**: The `-h FD` pattern allows passing passwords
+   from a pipe without command-line exposure. Lower priority but useful for
+   automation.
+
+3. **mlock() for password buffers**: Neither FreeBSD nor our implementation
+   uses `mlock()` to prevent password data from being swapped to disk.
+   OpenBSD doesn't either (they rely on encrypted swap). Consider adding
+   as defense-in-depth.
+
+## NetBSD Patterns
+
+NetBSD's user management follows similar patterns to FreeBSD. Key
+differences:
+
+- Uses `vipw(8)` for direct passwd editing (different approach)
+- Stricter POSIX compliance in username validation
+- Similar lack of memory hardening
+
+## Recommendations for shadow-rs
+
+All high-value items from BSD review are already tracked:
+
+- **mlock()**: Future work (docs/SECURITY-HARDENING.md)
+- **Samba usernames**: Could add `--badname` flag (matches GNU `useradd --badname`)
+- **Password fd input**: Low priority feature
+
+No critical security gaps found relative to FreeBSD/NetBSD implementations.
+shadow-rs is already more hardened than both.
+
+## References
+
+- FreeBSD pw: https://cgit.freebsd.org/src/tree/usr.sbin/pw/
+- NetBSD user management: https://cvsweb.netbsd.org/bsdweb.cgi/src/usr.sbin/user/
diff --git a/docs/man/chage.1.md b/docs/man/chage.1.md
new file mode 100644
index 0000000..3bffc9b
--- /dev/null
+++ b/docs/man/chage.1.md
@@ -0,0 +1,70 @@
+# chage(1) - change user password expiry information
+
+## NAME
+
+chage - change user password expiry information
+
+## SYNOPSIS
+
+**chage** [*options*] *LOGIN*
+
+## DESCRIPTION
+
+The **chage** command changes the number of days between password changes
+and the date of the last password change. This information is used by
+the system to determine when a user must change their password.
+
+## OPTIONS
+
+**-d**, **--lastday** *LAST_DAY*
+:   Set the date of the last password change. The date may be expressed
+    as a date (YYYY-MM-DD) or as the number of days since January 1, 1970.
+    A value of -1 removes the last-change date requirement.
+
+**-E**, **--expiredate** *EXPIRE_DATE*
+:   Set the account expiration date. The date may be expressed as a date
+    (YYYY-MM-DD) or as the number of days since January 1, 1970.
+    A value of -1 removes the expiration date.
+
+**-I**, **--inactive** *INACTIVE*
+:   Set the number of days of inactivity after a password has expired
+    before the account is locked. A value of -1 removes the inactivity
+    requirement.
+
+**-l**, **--list**
+:   Show account aging information.
+
+**-m**, **--mindays** *MIN_DAYS*
+:   Set the minimum number of days between password changes. A value
+    of -1 removes the minimum days requirement.
+
+**-M**, **--maxdays** *MAX_DAYS*
+:   Set the maximum number of days during which a password is valid.
+    A value of -1 removes the maximum days requirement.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-W**, **--warndays** *WARN_DAYS*
+:   Set the number of days of warning before a password change is
+    required. A value of -1 removes the warning.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Permission denied.
+
+**2**
+:   Invalid command syntax.
+
+## FILES
+
+/etc/shadow
+:   Secure user account information.
+
+## SEE ALSO
+
+passwd(1), passwd(5), shadow(5)
diff --git a/docs/man/chfn.1.md b/docs/man/chfn.1.md
new file mode 100644
index 0000000..e819353
--- /dev/null
+++ b/docs/man/chfn.1.md
@@ -0,0 +1,60 @@
+# chfn(1) - change user finger information
+
+## NAME
+
+chfn - change real user name and information
+
+## SYNOPSIS
+
+**chfn** [*options*] [*LOGIN*]
+
+## DESCRIPTION
+
+The **chfn** command changes the user finger information stored in the
+GECOS field of /etc/passwd. This information is typically displayed by
+the **finger**(1) program and includes the user's full name, office room
+number, and phone numbers.
+
+A normal user may only change their own finger information; the superuser
+may change the information for any user. Only the superuser may change
+the "other" field.
+
+At least one option flag (**-f**, **-r**, **-w**, **-h**, or **-o**) must
+be specified.
+
+## OPTIONS
+
+**-f**, **--full-name** *FULL_NAME*
+:   Change the user's full name.
+
+**-h**, **--home-phone** *HOME_PHONE*
+:   Change the user's home phone number.
+
+**-o**, **--other** *OTHER*
+:   Change the user's other GECOS information. Only root may set this field.
+
+**-r**, **--room** *ROOM*
+:   Change the user's room number.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-w**, **--work-phone** *WORK_PHONE*
+:   Change the user's office phone number.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Permission denied or operation failed.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+## SEE ALSO
+
+chsh(1), finger(1), passwd(5)
diff --git a/docs/man/chpasswd.8.md b/docs/man/chpasswd.8.md
new file mode 100644
index 0000000..11840ae
--- /dev/null
+++ b/docs/man/chpasswd.8.md
@@ -0,0 +1,56 @@
+# chpasswd(8) - update passwords in batch mode
+
+## NAME
+
+chpasswd - update passwords in batch mode
+
+## SYNOPSIS
+
+**chpasswd** [*options*]
+
+## DESCRIPTION
+
+The **chpasswd** command reads a list of username:password pairs from
+standard input and uses this information to update a group of existing
+users. Each line is of the format:
+
+    username:password
+
+By default the password is expected to be in cleartext (not yet
+supported in shadow-rs; use **-e**). With the **-e** flag, the password
+is expected to be already encrypted (pre-hashed).
+
+## OPTIONS
+
+**-c**, **--crypt-method** *METHOD*
+:   Use the specified crypt method. Supported values: SHA256, SHA512,
+    YESCRYPT, DES, MD5.
+
+**-e**, **--encrypted**
+:   Supplied passwords are already encrypted (pre-hashed).
+
+**-m**, **--md5**
+:   Use MD5 encryption for cleartext passwords (deprecated).
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-s**, **--sha-rounds** *ROUNDS*
+:   Use the specified number of rounds for SHA256/SHA512 encryption.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Permission denied, invalid input, file busy, or unexpected failure.
+
+## FILES
+
+/etc/shadow
+:   Secure user account information.
+
+## SEE ALSO
+
+passwd(1), passwd(5), shadow(5)
diff --git a/docs/man/chsh.1.md b/docs/man/chsh.1.md
new file mode 100644
index 0000000..430b9a3
--- /dev/null
+++ b/docs/man/chsh.1.md
@@ -0,0 +1,50 @@
+# chsh(1) - change login shell
+
+## NAME
+
+chsh - change login shell
+
+## SYNOPSIS
+
+**chsh** [*options*] [*LOGIN*]
+
+## DESCRIPTION
+
+The **chsh** command changes the user login shell. This determines the
+name of the user's initial login command. A normal user may only change
+the login shell for their own account; the superuser may change the login
+shell for any account.
+
+The new shell must be listed in /etc/shells unless the caller is root.
+
+## OPTIONS
+
+**-l**, **--list-shells**
+:   Print the list of shells listed in /etc/shells and exit.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-s**, **--shell** *SHELL*
+:   Set the login shell to *SHELL*. The shell must be an absolute path
+    and must be listed in /etc/shells (unless the caller is root).
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Permission denied or operation failed.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+/etc/shells
+:   List of valid login shells.
+
+## SEE ALSO
+
+chfn(1), login(1), passwd(5), shells(5)
diff --git a/docs/man/groupadd.8.md b/docs/man/groupadd.8.md
new file mode 100644
index 0000000..1a0d14c
--- /dev/null
+++ b/docs/man/groupadd.8.md
@@ -0,0 +1,80 @@
+# groupadd(8) - create a new group
+
+## NAME
+
+groupadd - create a new group
+
+## SYNOPSIS
+
+**groupadd** [*options*] *GROUP*
+
+## DESCRIPTION
+
+The **groupadd** command creates a new group account using the values
+specified on the command line plus the default values from the system.
+The new group will be entered into the system files (/etc/group and
+/etc/gshadow) as needed.
+
+## OPTIONS
+
+**-f**, **--force**
+:   Exit successfully if the group already exists, and cancel **-g** if
+    the GID is already used (a new GID will be allocated instead).
+
+**-g**, **--gid** *GID*
+:   Use *GID* for the new group.
+
+**-K**, **--key** *KEY=VALUE*
+:   Override /etc/login.defs defaults (GID_MIN, GID_MAX, SYS_GID_MIN,
+    SYS_GID_MAX). Can be specified multiple times.
+
+**-o**, **--non-unique**
+:   Allow creating a group with a non-unique (duplicate) GID.
+
+**-p**, **--password** *PASSWORD*
+:   Set the encrypted password for the new group.
+
+**-P**, **--prefix** *PREFIX_DIR*
+:   Use *PREFIX_DIR* as a prefix for system file paths.
+
+**-r**, **--system**
+:   Create a system group (allocated from the system GID range defined
+    in /etc/login.defs).
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**2**
+:   Invalid command syntax.
+
+**3**
+:   Invalid argument to option.
+
+**4**
+:   GID already in use (and no **-o** or **-f**).
+
+**9**
+:   Group name already in use.
+
+**10**
+:   Cannot update group file.
+
+## FILES
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information.
+
+/etc/login.defs
+:   Shadow password suite configuration.
+
+## SEE ALSO
+
+groupdel(8), groupmod(8), login.defs(5)
diff --git a/docs/man/groupdel.8.md b/docs/man/groupdel.8.md
new file mode 100644
index 0000000..4159884
--- /dev/null
+++ b/docs/man/groupdel.8.md
@@ -0,0 +1,54 @@
+# groupdel(8) - delete a group
+
+## NAME
+
+groupdel - delete a group
+
+## SYNOPSIS
+
+**groupdel** [*options*] *GROUP*
+
+## DESCRIPTION
+
+The **groupdel** command modifies the system account files, deleting all
+entries that refer to *GROUP*. The named group must exist.
+
+You may not remove the primary group of any existing user. You must
+remove the user before you remove the group.
+
+## OPTIONS
+
+**-P**, **--prefix** *PREFIX_DIR*
+:   Use *PREFIX_DIR* as a prefix for system file paths.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**2**
+:   Invalid command syntax.
+
+**6**
+:   Group does not exist.
+
+**8**
+:   Cannot remove a user's primary group.
+
+**10**
+:   Cannot update group file.
+
+## FILES
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information.
+
+## SEE ALSO
+
+groupadd(8), groupmod(8), userdel(8)
diff --git a/docs/man/groupmod.8.md b/docs/man/groupmod.8.md
new file mode 100644
index 0000000..0d90da2
--- /dev/null
+++ b/docs/man/groupmod.8.md
@@ -0,0 +1,70 @@
+# groupmod(8) - modify a group definition
+
+## NAME
+
+groupmod - modify a group definition
+
+## SYNOPSIS
+
+**groupmod** [*options*] *GROUP*
+
+## DESCRIPTION
+
+The **groupmod** command modifies the definition of the specified
+*GROUP* by modifying the appropriate entries in the group and gshadow
+databases.
+
+## OPTIONS
+
+**-g**, **--gid** *GID*
+:   Change the group ID to *GID*.
+
+**-n**, **--new-name** *NEW_GROUP*
+:   Change the name of the group to *NEW_GROUP*.
+
+**-o**, **--non-unique**
+:   Allow using a non-unique (duplicate) GID when used with **-g**.
+
+**-p**, **--password** *PASSWORD*
+:   Change the group password to the encrypted *PASSWORD*.
+
+**-P**, **--prefix** *PREFIX_DIR*
+:   Use *PREFIX_DIR* as a prefix for system file paths.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**2**
+:   Invalid command syntax.
+
+**3**
+:   Invalid argument to option.
+
+**4**
+:   GID already in use.
+
+**6**
+:   Group does not exist.
+
+**9**
+:   Group name already in use.
+
+**10**
+:   Cannot update group file.
+
+## FILES
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information.
+
+## SEE ALSO
+
+groupadd(8), groupdel(8)
diff --git a/docs/man/grpck.8.md b/docs/man/grpck.8.md
new file mode 100644
index 0000000..21758b8
--- /dev/null
+++ b/docs/man/grpck.8.md
@@ -0,0 +1,68 @@
+# grpck(8) - verify integrity of group files
+
+## NAME
+
+grpck - verify integrity of group files
+
+## SYNOPSIS
+
+**grpck** [*options*] [*group* [*gshadow*]]
+
+## DESCRIPTION
+
+The **grpck** command verifies the integrity of the group information.
+It checks that all entries in /etc/group and (optionally) /etc/gshadow
+have the proper format and contain valid data.
+
+Checks performed include:
+
+- Correct number of fields
+- Unique group names
+- Valid GID values
+- Matching group/gshadow entries
+
+## OPTIONS
+
+**-q**, **--quiet**
+:   Report only errors, suppress warnings.
+
+**-r**, **--read-only**
+:   Display errors and warnings but do not modify files.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-s**, **--sort**
+:   Sort entries by GID.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**2**
+:   One or more bad group entries.
+
+**3**
+:   Cannot open files.
+
+**4**
+:   Cannot lock files.
+
+**5**
+:   Cannot update files.
+
+**6**
+:   Cannot sort files.
+
+## FILES
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information.
+
+## SEE ALSO
+
+groupadd(8), groupdel(8), groupmod(8), pwck(8)
diff --git a/docs/man/newgrp.1.md b/docs/man/newgrp.1.md
new file mode 100644
index 0000000..8f4c2e7
--- /dev/null
+++ b/docs/man/newgrp.1.md
@@ -0,0 +1,50 @@
+# newgrp(1) - log in to a new group
+
+## NAME
+
+newgrp - log in to a new group
+
+## SYNOPSIS
+
+**newgrp** [*group*]
+
+## DESCRIPTION
+
+The **newgrp** command is used to change the current group ID during a
+login session. If the optional *group* argument is given, the effective
+group ID is changed to that group; otherwise the effective group ID is
+changed to the user's primary group from /etc/passwd.
+
+If the user is not a member of the specified group, and the group has a
+password set in /etc/gshadow, the user will be prompted for the group
+password. Root always has access to any group without a password prompt.
+
+A new shell is started with the changed group ID. The shell is
+determined by the **SHELL** environment variable, falling back to
+/bin/sh.
+
+## OPTIONS
+
+None. Only an optional positional group name argument is accepted.
+
+## EXIT STATUS
+
+**0**
+:   Success (though note that **newgrp** replaces the current process
+    with a new shell via **execv**(2), so exit status 0 is not normally
+    returned to the caller).
+
+**1**
+:   Permission denied, group not found, or unable to execute shell.
+
+## FILES
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information (for group passwords).
+
+## SEE ALSO
+
+groups(1), id(1), login(1), sg(1), group(5), gshadow(5)
diff --git a/docs/man/passwd.1.md b/docs/man/passwd.1.md
new file mode 100644
index 0000000..f7607ee
--- /dev/null
+++ b/docs/man/passwd.1.md
@@ -0,0 +1,104 @@
+# passwd(1) - change user password
+
+## NAME
+
+passwd - change user password
+
+## SYNOPSIS
+
+**passwd** [*options*] [*LOGIN*]
+
+## DESCRIPTION
+
+The **passwd** command changes passwords for user accounts. A normal user
+may only change the password for their own account; the superuser may
+change the password for any account. **passwd** also changes the account
+or associated password validity period.
+
+When invoked without a LOGIN argument, **passwd** changes the password for
+the current user.
+
+## OPTIONS
+
+**-a**, **--all**
+:   Report password status on all accounts. Requires **-S**.
+
+**-d**, **--delete**
+:   Delete the password for the named account. This makes the account
+    passwordless.
+
+**-e**, **--expire**
+:   Immediately expire the password for the named account. This forces
+    the user to change their password at next login.
+
+**-i**, **--inactive** *INACTIVE*
+:   Set the number of days of inactivity after a password has expired
+    before the account is locked.
+
+**-k**, **--keep-tokens**
+:   Change password only if expired.
+
+**-l**, **--lock**
+:   Lock the password of the named account. This prepends a '!' to the
+    encrypted password, effectively disabling the password.
+
+**-n**, **--mindays** *MIN_DAYS*
+:   Set the minimum number of days between password changes.
+
+**-q**, **--quiet**
+:   Quiet mode.
+
+**-r**, **--repository** *REPOSITORY*
+:   Change password in the named repository.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory and use the configuration
+    files from the *CHROOT_DIR* directory.
+
+**-P**, **--prefix** *PREFIX_DIR*
+:   Use *PREFIX_DIR* as a prefix for system file paths.
+
+**-S**, **--status**
+:   Display account status information. The status information consists
+    of 7 fields: login name, password status (L=locked, NP=no password,
+    P=usable password), date of last password change, minimum age,
+    maximum age, warning period, and inactivity period.
+
+**-s**, **--stdin**
+:   Read the new password token from standard input.
+
+**-u**, **--unlock**
+:   Unlock the password of the named account. This removes the '!' prefix
+    from the encrypted password.
+
+**-w**, **--warndays** *WARN_DAYS*
+:   Set the number of days of warning before a password change is required.
+
+**-x**, **--maxdays** *MAX_DAYS*
+:   Set the maximum number of days a password remains valid.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Permission denied or operation failed.
+
+**2**
+:   Invalid command syntax.
+
+**5**
+:   Password file busy.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+/etc/shadow
+:   Secure user account information.
+
+## SEE ALSO
+
+chage(1), chpasswd(8), login.defs(5), shadow(5), pwck(8)
diff --git a/docs/man/pwck.8.md b/docs/man/pwck.8.md
new file mode 100644
index 0000000..ad290eb
--- /dev/null
+++ b/docs/man/pwck.8.md
@@ -0,0 +1,74 @@
+# pwck(8) - verify integrity of password files
+
+## NAME
+
+pwck - verify integrity of password files
+
+## SYNOPSIS
+
+**pwck** [*options*] [*passwd* [*shadow*]]
+
+## DESCRIPTION
+
+The **pwck** command verifies the integrity of the system authentication
+information. It checks that all entries in /etc/passwd and /etc/shadow
+have the proper format and contain valid data.
+
+Checks performed include:
+
+- Correct number of fields
+- Unique and valid user names
+- Valid user and group identifiers
+- Valid primary group
+- Valid home directory
+- Valid login shell
+- Matching passwd/shadow entries
+
+## OPTIONS
+
+**-q**, **--quiet**
+:   Report only errors, suppress warnings.
+
+**-r**, **--read-only**
+:   Display errors and warnings but do not modify files.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-s**, **--sort**
+:   Sort entries by UID.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Invalid command syntax.
+
+**2**
+:   One or more bad password entries.
+
+**3**
+:   Cannot open files.
+
+**4**
+:   Cannot lock files.
+
+**5**
+:   Cannot update files.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+/etc/shadow
+:   Secure user account information.
+
+/etc/group
+:   Group account information.
+
+## SEE ALSO
+
+passwd(5), shadow(5), grpck(8)
diff --git a/docs/man/useradd.8.md b/docs/man/useradd.8.md
new file mode 100644
index 0000000..ffb62c1
--- /dev/null
+++ b/docs/man/useradd.8.md
@@ -0,0 +1,136 @@
+# useradd(8) - create a new user
+
+## NAME
+
+useradd - create a new user or update default new user information
+
+## SYNOPSIS
+
+**useradd** [*options*] *LOGIN*
+**useradd** **-D** [*options*]
+
+## DESCRIPTION
+
+The **useradd** command creates a new user account using the values
+specified on the command line plus the default values from the system.
+The new user account will be entered into the system files as needed,
+the home directory will be created, and initial files copied, depending
+on the command line options.
+
+When invoked with the **-D** flag, **useradd** displays or updates the
+default values used for creating new accounts.
+
+## OPTIONS
+
+**-c**, **--comment** *COMMENT*
+:   Set the GECOS field of the new account.
+
+**-d**, **--home-dir** *HOME_DIR*
+:   Set the home directory of the new account.
+
+**-D**, **--defaults**
+:   Print or change default useradd configuration.
+
+**-e**, **--expiredate** *EXPIRE_DATE*
+:   Set the expiration date of the new account (YYYY-MM-DD).
+
+**-f**, **--inactive** *INACTIVE*
+:   Set the password inactivity period of the new account.
+
+**-g**, **--gid** *GROUP*
+:   Set the name or numeric ID of the primary group of the new account.
+
+**-G**, **--groups** *GROUPS*
+:   Set the list of supplementary groups of the new account (comma-separated).
+
+**-k**, **--skel** *SKEL_DIR*
+:   Specify the skeleton directory (default: /etc/skel).
+
+**-m**, **--create-home**
+:   Create the user's home directory if it does not exist.
+
+**-M**, **--no-create-home**
+:   Do not create the user's home directory.
+
+**-N**, **--no-user-group**
+:   Do not create a group with the same name as the user.
+
+**-o**, **--non-unique**
+:   Allow creating users with duplicate (non-unique) UIDs. Requires **-u**.
+
+**-p**, **--password** *PASSWORD*
+:   Set the encrypted password of the new account.
+
+**-r**, **--system**
+:   Create a system account.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-s**, **--shell** *SHELL*
+:   Set the login shell of the new account.
+
+**-u**, **--uid** *UID*
+:   Set the user ID of the new account.
+
+**-U**, **--user-group**
+:   Create a group with the same name as the user (default behavior).
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Cannot update password file.
+
+**2**
+:   Invalid command syntax.
+
+**3**
+:   Invalid argument to option.
+
+**4**
+:   UID already in use (and no **-o**).
+
+**6**
+:   Specified group does not exist.
+
+**9**
+:   Username already in use.
+
+**10**
+:   Cannot update group file.
+
+**12**
+:   Cannot create home directory.
+
+**14**
+:   Cannot update SELinux user mapping.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+/etc/shadow
+:   Secure user account information.
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information.
+
+/etc/login.defs
+:   Shadow password suite configuration.
+
+/etc/default/useradd
+:   Default values for account creation.
+
+/etc/skel
+:   Directory containing default files.
+
+## SEE ALSO
+
+userdel(8), usermod(8), groupadd(8), login.defs(5)
diff --git a/docs/man/userdel.8.md b/docs/man/userdel.8.md
new file mode 100644
index 0000000..1bdb546
--- /dev/null
+++ b/docs/man/userdel.8.md
@@ -0,0 +1,67 @@
+# userdel(8) - delete a user account
+
+## NAME
+
+userdel - delete a user account and related files
+
+## SYNOPSIS
+
+**userdel** [*options*] *LOGIN*
+
+## DESCRIPTION
+
+The **userdel** command modifies the system account files, deleting all
+entries that refer to the user name *LOGIN*. The named user must exist.
+
+The user's entry is removed from /etc/passwd and /etc/shadow. The user
+is also removed from membership lists in /etc/group and /etc/gshadow.
+
+## OPTIONS
+
+**-f**, **--force**
+:   Force removal of the account even if the user is still logged in.
+    Also forces removal of the home directory and mail spool.
+
+**-P**, **--prefix** *PREFIX_DIR*
+:   Use *PREFIX_DIR* as a prefix for system file paths.
+
+**-r**, **--remove**
+:   Remove the user's home directory and mail spool.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Cannot update password file.
+
+**2**
+:   Invalid command syntax.
+
+**10**
+:   Cannot update group file.
+
+**12**
+:   Cannot remove home directory.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+/etc/shadow
+:   Secure user account information.
+
+/etc/group
+:   Group account information.
+
+/etc/gshadow
+:   Secure group account information.
+
+## SEE ALSO
+
+useradd(8), usermod(8), groupdel(8)
diff --git a/docs/man/usermod.8.md b/docs/man/usermod.8.md
new file mode 100644
index 0000000..943ec95
--- /dev/null
+++ b/docs/man/usermod.8.md
@@ -0,0 +1,93 @@
+# usermod(8) - modify a user account
+
+## NAME
+
+usermod - modify a user account
+
+## SYNOPSIS
+
+**usermod** [*options*] *LOGIN*
+
+## DESCRIPTION
+
+The **usermod** command modifies the system account files to reflect the
+changes that are specified on the command line.
+
+## OPTIONS
+
+**-a**, **--append**
+:   Append the user to the supplementary group(s) specified by **-G**.
+    Use only with the **-G** option.
+
+**-c**, **--comment** *COMMENT*
+:   Set the new value of the user's GECOS field.
+
+**-d**, **--home** *HOME_DIR*
+:   Set the new home directory for the user.
+
+**-e**, **--expiredate** *EXPIRE_DATE*
+:   Set the account expiration date.
+
+**-f**, **--inactive** *INACTIVE*
+:   Set the password inactive period.
+
+**-g**, **--gid** *GROUP*
+:   Set the new primary group ID (numeric).
+
+**-G**, **--groups** *GROUPS*
+:   Set the list of supplementary groups (comma-separated). If the **-a**
+    option is not used, the user is removed from all groups not listed.
+
+**-l**, **--login** *NEW_LOGIN*
+:   Change the user's login name.
+
+**-L**, **--lock**
+:   Lock the user's password by prepending a '!' to the shadow password.
+
+**-P**, **--prefix** *PREFIX_DIR*
+:   Use *PREFIX_DIR* as a prefix for system file paths.
+
+**-R**, **--root** *CHROOT_DIR*
+:   Apply changes in the *CHROOT_DIR* directory.
+
+**-s**, **--shell** *SHELL*
+:   Set the new login shell.
+
+**-u**, **--uid** *UID*
+:   Set the new numeric user ID.
+
+**-U**, **--unlock**
+:   Unlock the user's password by removing the '!' prefix from the
+    shadow password.
+
+## EXIT STATUS
+
+**0**
+:   Success.
+
+**1**
+:   Cannot update password file.
+
+**2**
+:   Invalid command syntax.
+
+**4**
+:   UID already in use.
+
+**6**
+:   User does not exist.
+
+## FILES
+
+/etc/passwd
+:   User account information.
+
+/etc/shadow
+:   Secure user account information.
+
+/etc/group
+:   Group account information.
+
+## SEE ALSO
+
+useradd(8), userdel(8), groupmod(8), passwd(1)
diff --git a/src/shadow-core/src/skel.rs b/src/shadow-core/src/skel.rs
index 5059d01..c1ab57e 100644
--- a/src/shadow-core/src/skel.rs
+++ b/src/shadow-core/src/skel.rs
@@ -44,6 +44,12 @@ fn copy_dir_recursive(src: &Path, dst: &Path, uid: u32, gid: u32) -> Result<(),
         if file_type.is_dir() {
             std::fs::create_dir_all(&dst_path)
                 .map_err(|e| ShadowError::IoPath(e, dst_path.clone()))?;
+            // Preserve the source directory's permissions.
+            let src_perms = std::fs::metadata(&src_path)
+                .map_err(|e| ShadowError::IoPath(e, src_path.clone()))?
+                .permissions();
+            std::fs::set_permissions(&dst_path, src_perms)
+                .map_err(|e| ShadowError::IoPath(e, dst_path.clone()))?;
             copy_dir_recursive(&src_path, &dst_path, uid, gid)?;
         } else if file_type.is_symlink() {
             let target = std::fs::read_link(&src_path)
diff --git a/src/uu/useradd/src/useradd.rs b/src/uu/useradd/src/useradd.rs
index 279eac5..584967e 100644
--- a/src/uu/useradd/src/useradd.rs
+++ b/src/uu/useradd/src/useradd.rs
@@ -203,12 +203,19 @@ fn parse_expire_date(s: &str) -> Result<Option<i64>, UseraddError> {
         UseraddError::BadArgument(format!("invalid date '{s}' (expected YYYY-MM-DD)"))
     })?;
 
-    if !(1..=12).contains(&month) || !(1..=31).contains(&day) || year < 1970 {
+    if !(1..=12).contains(&month) || year < 1970 {
         return Err(UseraddError::BadArgument(format!(
             "invalid date '{s}' (expected YYYY-MM-DD with valid ranges)"
         )));
     }
 
+    let max_day = days_in_month(year, month);
+    if !(1..=max_day).contains(&day) {
+        return Err(UseraddError::BadArgument(format!(
+            "invalid date '{s}' (day {day} out of range for month {month})"
+        )));
+    }
+
     // Convert to days since epoch using a simple calendar calculation.
     // This is sufficient for the date ranges used by shadow-utils.
     let days = days_since_epoch(year, month, day);
@@ -229,6 +236,28 @@ fn days_since_epoch(year: i64, month: i64, day: i64) -> i64 {
     era * 146_097 + doe - 719_468
 }
 
+/// Whether `year` is a leap year in the Gregorian calendar.
+fn is_leap_year(year: i64) -> bool {
+    (year % 4 == 0 && year % 100 != 0) || year % 400 == 0
+}
+
+/// Number of days in a given month (1-indexed) for `year`.
+fn days_in_month(year: i64, month: i64) -> i64 {
+    match month {
+        1 | 3 | 5 | 7 | 8 | 10 | 12 => 31,
+        4 | 6 | 9 | 11 => 30,
+        2 => {
+            if is_leap_year(year) {
+                29
+            } else {
+                28
+            }
+        }
+        // Month range is already validated before calling this function.
+        _ => 0,
+    }
+}
+
 /// Current date as days since epoch.
 #[allow(clippy::cast_possible_wrap)]
 fn today_days_since_epoch() -> i64 {
@@ -574,7 +603,9 @@ fn do_useradd(opts: &UseraddOptions) -> UResult<()> {
 
     // Step 15: Create home directory and copy skel.
     if opts.create_home {
-        create_home_directory(&home_dir, &opts.skel_dir, uid, gid)?;
+        let resolved_home = opts.root.resolve(&home_dir);
+        let resolved_skel = opts.root.resolve(&opts.skel_dir);
+        create_home_directory(&resolved_home, &resolved_skel, uid, gid)?;
     }
 
     // Step 16: Invalidate nscd caches.
@@ -809,22 +840,23 @@ fn add_to_supplementary_groups(
 // ---------------------------------------------------------------------------
 
 /// Create the home directory and copy skeleton files.
-fn create_home_directory(home_dir: &str, skel_dir: &str, uid: u32, gid: u32) -> UResult<()> {
-    let home_path = Path::new(home_dir);
-
+///
+/// Paths must already be resolved through `SysRoot` by the caller.
+fn create_home_directory(home_path: &Path, skel_path: &Path, uid: u32, gid: u32) -> UResult<()> {
     // Use create_dir (not create_dir_all) to avoid TOCTOU between exists() and mkdir().
     match std::fs::create_dir(home_path) {
         Ok(()) => {}
         Err(e) if e.kind() == std::io::ErrorKind::AlreadyExists => {
             uucore::show_warning!(
                 "home directory '{}' already exists -- not copying from skel directory",
-                home_dir
+                home_path.display()
             );
             return Ok(());
         }
         Err(e) => {
             return Err(UseraddError::CannotCreateHome(format!(
-                "cannot create directory '{home_dir}': {e}"
+                "cannot create directory '{}': {e}",
+                home_path.display()
             ))
             .into());
         }
@@ -832,19 +864,26 @@ fn create_home_directory(home_dir: &str, skel_dir: &str, uid: u32, gid: u32) ->
 
     // Set permissions to 0700 (home directories should be private by default).
     std::fs::set_permissions(home_path, std::fs::Permissions::from_mode(0o700)).map_err(|e| {
-        UseraddError::CannotCreateHome(format!("cannot set permissions on '{home_dir}': {e}"))
+        UseraddError::CannotCreateHome(format!(
+            "cannot set permissions on '{}': {e}",
+            home_path.display()
+        ))
     })?;
 
     // Set ownership.
     std::os::unix::fs::chown(home_path, Some(uid), Some(gid)).map_err(|e| {
-        UseraddError::CannotCreateHome(format!("cannot set ownership on '{home_dir}': {e}"))
+        UseraddError::CannotCreateHome(format!(
+            "cannot set ownership on '{}': {e}",
+            home_path.display()
+        ))
     })?;
 
     // Copy skeleton directory contents.
-    let skel_path = Path::new(skel_dir);
     skel::copy_skel(skel_path, home_path, uid, gid).map_err(|e| {
         UseraddError::CannotCreateHome(format!(
-            "cannot copy skel '{skel_dir}' to '{home_dir}': {e}"
+            "cannot copy skel '{}' to '{}': {e}",
+            skel_path.display(),
+            home_path.display()
         ))
     })?;
 
@@ -1250,6 +1289,48 @@ mod tests {
         assert!(parse_expire_date("1969-12-31").is_err());
     }
 
+    #[test]
+    fn test_parse_expire_date_feb_31() {
+        assert!(parse_expire_date("2025-02-31").is_err());
+    }
+
+    #[test]
+    fn test_parse_expire_date_feb_29_non_leap() {
+        assert!(parse_expire_date("2025-02-29").is_err());
+    }
+
+    #[test]
+    fn test_parse_expire_date_feb_29_leap() {
+        assert!(parse_expire_date("2024-02-29").is_ok());
+    }
+
+    #[test]
+    fn test_parse_expire_date_apr_31() {
+        assert!(parse_expire_date("2025-04-31").is_err());
+    }
+
+    #[test]
+    fn test_parse_expire_date_apr_30() {
+        assert!(parse_expire_date("2025-04-30").is_ok());
+    }
+
+    #[test]
+    fn test_is_leap_year() {
+        assert!(is_leap_year(2000));
+        assert!(is_leap_year(2024));
+        assert!(!is_leap_year(1900));
+        assert!(!is_leap_year(2023));
+    }
+
+    #[test]
+    fn test_days_in_month_values() {
+        assert_eq!(days_in_month(2025, 1), 31);
+        assert_eq!(days_in_month(2025, 2), 28);
+        assert_eq!(days_in_month(2024, 2), 29);
+        assert_eq!(days_in_month(2025, 4), 30);
+        assert_eq!(days_in_month(2025, 12), 31);
+    }
+
     #[test]
     fn test_days_since_epoch_known_dates() {
         // 1970-01-01 = day 0
@@ -1605,12 +1686,14 @@ mod tests {
         let home = dir.path().join("home/testuser");
         let skel = dir.path().join("skel");
 
+        // Parent of home must exist (create_dir is intentionally used, not create_dir_all).
+        fs::create_dir_all(dir.path().join("home")).expect("create home parent");
+
         // Create skeleton directory with a file.
         fs::create_dir_all(&skel).expect("create skel");
         fs::write(skel.join(".bashrc"), "# bashrc\n").expect("write bashrc");
 
-        create_home_directory(&home.to_string_lossy(), &skel.to_string_lossy(), 1000, 1000)
-            .expect("create home");
+        create_home_directory(&home, &skel, 1000, 1000).expect("create home");
 
         assert!(home.exists());
         assert!(home.join(".bashrc").exists());
@@ -1632,7 +1715,7 @@ mod tests {
         fs::create_dir_all(&home).expect("create home");
 
         // Should succeed with a warning, not copy skel.
-        create_home_directory(&home.to_string_lossy(), "/nonexistent/skel", 1000, 1000)
+        create_home_directory(&home, Path::new("/nonexistent/skel"), 1000, 1000)
             .expect("should succeed for existing home");
     }
 
diff --git a/src/uu/userdel/src/userdel.rs b/src/uu/userdel/src/userdel.rs
index 9bd94ad..c83aee4 100644
--- a/src/uu/userdel/src/userdel.rs
+++ b/src/uu/userdel/src/userdel.rs
@@ -85,8 +85,11 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let login = matches
         .get_one::<String>(options::LOGIN)
         .expect("LOGIN is required");
-    let remove_home = matches.get_flag(options::REMOVE) || matches.get_flag(options::FORCE);
-    let prefix = matches.get_one::<String>(options::PREFIX).map(Path::new);
+    let remove_home = matches.get_flag(options::REMOVE);
+    let prefix = matches
+        .get_one::<String>(options::PREFIX)
+        .or_else(|| matches.get_one::<String>(options::ROOT))
+        .map(Path::new);
     let root = SysRoot::new(prefix);
 
     // Must be root.
diff --git a/src/uu/usermod/src/usermod.rs b/src/uu/usermod/src/usermod.rs
index 137886d..6b55c09 100644
--- a/src/uu/usermod/src/usermod.rs
+++ b/src/uu/usermod/src/usermod.rs
@@ -19,7 +19,7 @@ use shadow_core::lock::FileLock;
 use shadow_core::passwd::{self};
 use shadow_core::shadow::{self};
 use shadow_core::sysroot::SysRoot;
-use shadow_core::{atomic, nscd};
+use shadow_core::{atomic, nscd, validate};
 
 mod options {
     pub const COMMENT: &str = "comment";
@@ -88,7 +88,10 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let login = matches
         .get_one::<String>(options::USER)
         .expect("USER is required");
-    let prefix = matches.get_one::<String>(options::PREFIX).map(Path::new);
+    let prefix = matches
+        .get_one::<String>(options::PREFIX)
+        .or_else(|| matches.get_one::<String>(options::ROOT))
+        .map(Path::new);
     let root = SysRoot::new(prefix);
 
     if !nix::unistd::getuid().is_root() {
@@ -134,8 +137,11 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     if let Some(&gid) = matches.get_one::<u32>(options::GID) {
         entries[idx].gid = gid;
     }
-    if let Some(new_login) = matches.get_one::<String>(options::LOGIN) {
-        entries[idx].name.clone_from(new_login);
+    let new_login = matches.get_one::<String>(options::LOGIN);
+    if let Some(new_name) = new_login {
+        validate::validate_username(new_name)
+            .map_err(|e| UsermodError::CantUpdate(format!("invalid login name: {e}")))?;
+        entries[idx].name.clone_from(new_name);
     }
 
     let new_uid = entries[idx].uid;
@@ -160,7 +166,10 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let expire = matches.get_one::<String>(options::EXPIREDATE);
     let inactive = matches.get_one::<i64>(options::INACTIVE);
 
-    if shadow_path.exists() && (do_lock || do_unlock || expire.is_some() || inactive.is_some()) {
+    let login_changing = new_login.is_some();
+    if shadow_path.exists()
+        && (do_lock || do_unlock || expire.is_some() || inactive.is_some() || login_changing)
+    {
         let slock = FileLock::acquire(&shadow_path)
             .map_err(|e| UsermodError::CantUpdate(format!("cannot lock shadow: {e}")))?;
 
@@ -175,11 +184,22 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
                 s.unlock();
             }
             if let Some(exp) = expire {
-                s.expire_date = if exp == "-1" { None } else { exp.parse().ok() };
+                s.expire_date = if exp == "-1" || exp.is_empty() {
+                    None
+                } else {
+                    Some(exp.parse::<i64>().map_err(|_| {
+                        UsermodError::CantUpdate(format!(
+                            "invalid expire date '{exp}' (expected days since epoch)"
+                        ))
+                    })?)
+                };
             }
             if let Some(&i) = inactive {
                 s.inactive_days = if i < 0 { None } else { Some(i) };
             }
+            if let Some(new_name) = new_login {
+                s.name.clone_from(new_name);
+            }
         }
 
         atomic::atomic_write(&shadow_path, |f| shadow::write_shadow(&se, f))
@@ -187,6 +207,32 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         drop(slock);
     }
 
+    // Rename user in group membership lists when --login changes the name.
+    if let Some(new_name) = new_login {
+        let group_path = root.group_path();
+        if group_path.exists() {
+            let glock = FileLock::acquire(&group_path)
+                .map_err(|e| UsermodError::CantUpdate(format!("cannot lock group: {e}")))?;
+
+            let mut ge = group::read_group_file(&group_path)
+                .map_err(|e| UsermodError::CantUpdate(format!("{e}")))?;
+
+            let mut changed = false;
+            for g in &mut ge {
+                if let Some(m) = g.members.iter_mut().find(|m| **m == *login) {
+                    m.clone_from(new_name);
+                    changed = true;
+                }
+            }
+
+            if changed {
+                atomic::atomic_write(&group_path, |f| group::write_group(&ge, f))
+                    .map_err(|e| UsermodError::CantUpdate(format!("{e}")))?;
+            }
+            drop(glock);
+        }
+    }
+
     // Group modifications.
     if let Some(groups_str) = matches.get_one::<String>(options::GROUPS) {
         let group_path = root.group_path();