diff --git a/sys/tests/sys-tests.rs b/sys/tests/sys-tests.rs
index f746f40c..e12f026c 100644
--- a/sys/tests/sys-tests.rs
+++ b/sys/tests/sys-tests.rs
@@ -2,3 +2,4 @@ mod getconf;
 mod ipcrm;
 mod ipcs;
 mod uname;
+mod who;
diff --git a/sys/tests/who/mod.rs b/sys/tests/who/mod.rs
new file mode 100644
index 00000000..9d6582bb
--- /dev/null
+++ b/sys/tests/who/mod.rs
@@ -0,0 +1,170 @@
+//
+// Copyright (c) 2024 Jeff Garzik
+//
+// This file is part of the posixutils-rs project covered under
+// the MIT License.  For the full license text, please see the LICENSE
+// file in the root directory of this project.
+// SPDX-License-Identifier: MIT
+//
+
+use plib::testing::{run_test_with_checker, TestPlan};
+use std::process::Output;
+
+fn run_who_test(args: Vec<&str>, expected_exit_code: i32, check_fn: fn(&TestPlan, &Output)) {
+    let plan = TestPlan {
+        cmd: "who".to_string(),
+        args: args.iter().map(|&s| s.to_string()).collect(),
+        stdin_data: String::new(),
+        expected_out: String::new(),
+        expected_err: String::new(),
+        expected_exit_code,
+    };
+    run_test_with_checker(plan, check_fn);
+}
+
+// Checker functions
+fn check_exit_success(_: &TestPlan, output: &Output) {
+    assert!(output.status.success(), "Expected successful exit");
+}
+
+fn check_has_column_headings(_: &TestPlan, output: &Output) {
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let lines: Vec<&str> = stdout.lines().collect();
+
+    // Should have at least a header line
+    assert!(!lines.is_empty(), "Expected output with headings");
+
+    // First line should contain column headers
+    let first_line = lines[0].to_uppercase();
+    assert!(
+        first_line.contains("NAME") || first_line.contains("LINE") || first_line.contains("TIME"),
+        "Expected header line to contain NAME, LINE, or TIME"
+    );
+}
+
+fn check_summary_format(_: &TestPlan, output: &Output) {
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let lines: Vec<&str> = stdout.lines().collect();
+
+    // Summary format should have at least the "# users=" line
+    assert!(
+        lines.iter().any(|line| line.contains("# users=")),
+        "Expected '# users=' line in summary output"
+    );
+}
+
+fn check_output_has_terminal_state(_: &TestPlan, output: &Output) {
+    let stdout = String::from_utf8_lossy(&output.stdout);
+
+    // With -T, output should include terminal state characters (+, -, ?)
+    // Skip if no output (no logged in users)
+    if !stdout.trim().is_empty() {
+        let lines: Vec<&str> = stdout.lines().filter(|l| !l.trim().is_empty()).collect();
+        if !lines.is_empty() {
+            // At least one line should potentially have terminal state indicators
+            // The format should be: NAME STATE LINE TIME
+            // We can't guarantee specific output, but we can check structure
+            for line in lines {
+                // Each line should have multiple fields
+                let fields: Vec<&str> = line.split_whitespace().collect();
+                assert!(fields.len() >= 2, "Expected multiple fields in output");
+            }
+        }
+    }
+}
+
+#[test]
+fn who_no_args() {
+    // Default behavior: show logged in users
+    run_who_test(vec![], 0, check_exit_success);
+}
+
+#[test]
+fn who_short_format() {
+    // -s is the default, explicit test
+    run_who_test(vec!["-s"], 0, check_exit_success);
+}
+
+#[test]
+fn who_heading() {
+    // -H should print column headings
+    run_who_test(vec!["-H"], 0, check_has_column_headings);
+}
+
+#[test]
+fn who_summary() {
+    // -q should show summary format
+    run_who_test(vec!["-q"], 0, check_summary_format);
+}
+
+#[test]
+fn who_boot() {
+    // -b should show boot time
+    run_who_test(vec!["-b"], 0, check_exit_success);
+}
+
+#[test]
+fn who_dead() {
+    // -d should show dead processes
+    run_who_test(vec!["-d"], 0, check_exit_success);
+}
+
+#[test]
+fn who_login() {
+    // -l should show login processes
+    run_who_test(vec!["-l"], 0, check_exit_success);
+}
+
+#[test]
+fn who_process() {
+    // -p should show active processes spawned by init
+    run_who_test(vec!["-p"], 0, check_exit_success);
+}
+
+#[test]
+fn who_runlevel() {
+    // -r should show current runlevel
+    run_who_test(vec!["-r"], 0, check_exit_success);
+}
+
+#[test]
+fn who_time() {
+    // -t should show last system clock change
+    run_who_test(vec!["-t"], 0, check_exit_success);
+}
+
+#[test]
+fn who_terminals() {
+    // -T should show terminal state
+    run_who_test(vec!["-T"], 0, check_output_has_terminal_state);
+}
+
+#[test]
+fn who_users() {
+    // -u should show idle time for users
+    run_who_test(vec!["-u"], 0, check_exit_success);
+}
+
+#[test]
+fn who_all() {
+    // -a should enable all options
+    run_who_test(vec!["-a"], 0, check_exit_success);
+}
+
+#[test]
+fn who_combined_options() {
+    // Test combining options
+    run_who_test(vec!["-H", "-b"], 0, check_has_column_headings);
+}
+
+#[test]
+fn who_current_terminal() {
+    // -m should show only current terminal
+    run_who_test(vec!["-m"], 0, check_exit_success);
+}
+
+#[test]
+fn who_userproc() {
+    // --userproc should show normal user processes
+    run_who_test(vec!["--userproc"], 0, check_exit_success);
+}
diff --git a/sys/who.rs b/sys/who.rs
index d4106841..82e795c7 100644
--- a/sys/who.rs
+++ b/sys/who.rs
@@ -140,16 +140,50 @@ fn get_idle_time(line: &str) -> String {
     }
 }
 
+// Clean up the id field - take only first 4 chars or until first non-alphanumeric
+fn clean_id_field(id: &str) -> String {
+    id.chars()
+        .take_while(|c| c.is_alphanumeric() || *c == '~' || *c == '/')
+        .take(4)
+        .collect::<String>()
+}
+
+// Get the comment field to display for an entry
+fn get_comment_field(entry: &Utmpx) -> String {
+    let clean_id = clean_id_field(&entry.id);
+    if !clean_id.is_empty() && entry.typ != platform::USER_PROCESS {
+        format!("id={}", clean_id)
+    } else if !entry.host.is_empty() && entry.typ == platform::USER_PROCESS {
+        format!("({})", entry.host)
+    } else {
+        String::new()
+    }
+}
+
 fn print_fmt_short(args: &Args, entry: &Utmpx, line: &str) {
     if args.idle_time {
-        println!(
-            "{:<16} {:<12} {} {} {:>5}",
-            entry.user,
-            line,
-            fmt_timestamp(entry.timestamp),
-            get_idle_time(line),
-            entry.pid
-        );
+        let comment = get_comment_field(entry);
+
+        if comment.is_empty() {
+            println!(
+                "{:<16} {:<12} {} {} {:>5}",
+                entry.user,
+                line,
+                fmt_timestamp(entry.timestamp),
+                get_idle_time(line),
+                entry.pid
+            );
+        } else {
+            println!(
+                "{:<16} {:<12} {} {} {:>5} {}",
+                entry.user,
+                line,
+                fmt_timestamp(entry.timestamp),
+                get_idle_time(line),
+                entry.pid,
+                comment
+            );
+        }
     } else {
         println!(
             "{:<16} {:<12} {}",
@@ -163,15 +197,30 @@ fn print_fmt_short(args: &Args, entry: &Utmpx, line: &str) {
 fn print_fmt_term(args: &Args, entry: &Utmpx, line: &str) {
     let term_state = get_terminal_state(line);
     if args.idle_time {
-        println!(
-            "{:<16} {} {:<12} {} {} {:>5}",
-            entry.user,
-            term_state,
-            line,
-            fmt_timestamp(entry.timestamp),
-            get_idle_time(line),
-            entry.pid
-        );
+        let comment = get_comment_field(entry);
+
+        if comment.is_empty() {
+            println!(
+                "{:<16} {} {:<12} {} {} {:>5}",
+                entry.user,
+                term_state,
+                line,
+                fmt_timestamp(entry.timestamp),
+                get_idle_time(line),
+                entry.pid
+            );
+        } else {
+            println!(
+                "{:<16} {} {:<12} {} {} {:>5} {}",
+                entry.user,
+                term_state,
+                line,
+                fmt_timestamp(entry.timestamp),
+                get_idle_time(line),
+                entry.pid,
+                comment
+            );
+        }
     } else {
         println!(
             "{:<16} {} {:<12} {}",
@@ -216,6 +265,8 @@ fn print_entry(args: &Args, entry: &Utmpx) {
         || (args.login && entry.typ == platform::LOGIN_PROCESS)
         || (args.runlevel && entry.typ == platform::RUN_LVL)
         || (args.process && entry.typ == platform::INIT_PROCESS)
+        || (args.last_change
+            && (entry.typ == platform::OLD_TIME || entry.typ == platform::NEW_TIME))
     {
         selected = true;
     }
@@ -238,12 +289,47 @@ fn print_entry(args: &Args, entry: &Utmpx) {
 
 fn show_utmpx_entries(args: &Args) {
     if args.heading {
-        println!(
-            "{:<16} {:<12} {}",
-            gettext("NAME"),
-            gettext("LINE"),
-            gettext("TIME")
-        );
+        if args.idle_time && args.terminals {
+            // -H -u -T format
+            println!(
+                "{:<16} {} {:<12} {:<16} {:>5} {:>5} {}",
+                gettext("NAME"),
+                "",
+                gettext("LINE"),
+                gettext("TIME"),
+                gettext("IDLE"),
+                gettext("PID"),
+                gettext("COMMENT")
+            );
+        } else if args.idle_time {
+            // -H -u format
+            println!(
+                "{:<16} {:<12} {:<16} {:>5} {:>5} {}",
+                gettext("NAME"),
+                gettext("LINE"),
+                gettext("TIME"),
+                gettext("IDLE"),
+                gettext("PID"),
+                gettext("COMMENT")
+            );
+        } else if args.terminals {
+            // -H -T format
+            println!(
+                "{:<16} {} {:<12} {}",
+                gettext("NAME"),
+                "",
+                gettext("LINE"),
+                gettext("TIME")
+            );
+        } else {
+            // -H format
+            println!(
+                "{:<16} {:<12} {}",
+                gettext("NAME"),
+                gettext("LINE"),
+                gettext("TIME")
+            );
+        }
     }
 
     let entries = utmpx::load();