diff --git a/Cargo.lock b/Cargo.lock
index 2d88da5..a8c6f4e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -162,9 +162,9 @@ dependencies = [
 
 [[package]]
 name = "libc"
-version = "0.2.138"
+version = "0.2.139"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "db6d7e329c562c5dfab7a46a2afabc8b987ab9a4834c9d1ca04dc54c1546cef8"
+checksum = "201de327520df007757c1f0adce6e827fe8562fbc28bfd9c15571c66ca1f5f79"
 
 [[package]]
 name = "linux-raw-sys"
@@ -222,6 +222,7 @@ dependencies = [
  "clap_mangen",
  "data-encoding",
  "hostname",
+ "libc",
  "once_cell",
  "termcolor",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 85e3186..97eae97 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,6 +14,7 @@ clap_complete_nushell = "0.1.8"
 clap_mangen = "0.2.5"
 data-encoding = "2.3.3"
 hostname = { version = "0.3", features = ["set"] }
+libc = "0.2.139"
 once_cell = "1.16.0"
 termcolor = "1.1.3"
 
diff --git a/src/cmd/mountpoint/mod.rs b/src/cmd/mountpoint/mod.rs
index c20600f..8638cb0 100644
--- a/src/cmd/mountpoint/mod.rs
+++ b/src/cmd/mountpoint/mod.rs
@@ -1,5 +1,13 @@
 use super::Cmd;
 use clap::{Arg, ArgAction, Command};
+use std::{
+    error::Error,
+    fs::{self, File},
+    io::{self, BufRead, BufReader, ErrorKind},
+    os::linux::fs::MetadataExt,
+    path::PathBuf,
+    process,
+};
 
 #[derive(Debug)]
 pub struct Mountpoint {
@@ -21,14 +29,31 @@ impl Cmd for Mountpoint {
         Command::new(self.name)
             .about("see if a directory or file is a mountpoint")
             .author("Nathan Fisher")
+            .after_long_help(
+                "EXIT STATUS\n      \
+                0\n          \
+                success: the directory is a mountpoint, or device is a block\
+                device on --devno\n      \
+                1\n          \
+                failure: incorrect invocation, permissions or system error\
+                \n      32\n          \
+                failure: the directory is not a mountpoint, or device is not a \
+                block device on --devno"
+            )
             .args([
                 Arg::new("fs-devno")
-                    .help("Show the major/minor numbers of the device that is mounted on the given directory.")
+                    .help(
+                        "Show the major/minor numbers of the device that is \
+                          mounted on the given directory.",
+                    )
                     .short('d')
                     .long("fs-devno")
                     .action(ArgAction::SetTrue),
                 Arg::new("devno")
-                    .help("Show the major/minor numbers of the given blockdevice on standard output.")
+                    .help(
+                        "Show the major/minor numbers of the given blockdevice \
+                          on standard output.",
+                    )
                     .short('x')
                     .long("devno")
                     .conflicts_with("fs-devno")
@@ -38,14 +63,92 @@ impl Cmd for Mountpoint {
                     .short('q')
                     .long("quiet")
                     .action(ArgAction::SetTrue),
+                Arg::new("file").num_args(1).required(true),
             ])
     }
 
     fn run(&self, matches: Option<&clap::ArgMatches>) -> Result<(), Box<dyn std::error::Error>> {
-        unimplemented!();
+        let Some(matches) = matches else {
+            return Err(io::Error::new(ErrorKind::Other, "no input").into());
+        };
+        let file = matches.get_one::<String>("file").unwrap();
+        if matches.get_flag("fs-devno") {
+            match fs_devno(file)? {
+                Some(maj_min) => println!("{maj_min}"),
+                None => {
+                    println!("{file} is not a mountpoint");
+                    process::exit(32);
+                }
+            }
+        } else if matches.get_flag("devno") {
+            let devno = devno(file)?;
+            println!("{}:{}", devno.0, devno.1);
+        } else {
+            let val = is_mountpoint(file)?;
+            if val {
+                if !matches.get_flag("quiet") {
+                    println!("{file} is a mountpoint");
+                }
+                return Ok(());
+            } else {
+                if !matches.get_flag("quiet") {
+                    println!("{file} is not a mountpoint");
+                }
+                process::exit(32);
+            }
+        }
+        Ok(())
     }
 
     fn path(&self) -> Option<crate::Path> {
         self.path
     }
 }
+
+fn is_mountpoint(path: &str) -> Result<bool, Box<dyn Error>> {
+    let fd = File::open("/proc/mounts")?;
+    let reader = BufReader::new(fd);
+    for line in reader.lines() {
+        let line = line?;
+        if let Some(mntpt) = line.split_whitespace().skip(1).next() {
+            if mntpt == path {
+                return Ok(true);
+            }
+        }
+    }
+    Ok(false)
+}
+
+fn fs_devno(path: &str) -> Result<Option<String>, Box<dyn Error>> {
+    let p = PathBuf::from(path);
+    if !p.exists() {
+        let msg = format!("mountpoint: {path}: No such file or directory");
+        return Err(Box::new(io::Error::new(ErrorKind::Other, msg)));
+    }
+    let fd = File::open("/proc/self/mountinfo")?;
+    let reader = BufReader::new(fd);
+    for line in reader.lines() {
+        let line = line?;
+        let mut line = line.split_whitespace().skip(2);
+        if let Some(maj_min) = line.next() {
+            if let Some(mntpt) = line.skip(1).next() {
+                if mntpt == path {
+                    return Ok(Some(String::from(maj_min)));
+                }
+            }
+        }
+    }
+    Ok(None)
+}
+
+fn devno(path: &str) -> Result<(u32, u32), Box<dyn Error>> {
+    let meta = fs::metadata(path)?;
+    let rdev = meta.st_rdev();
+    if rdev == 0 {
+        let msg = format!("Mountpoint: Error: {path} is not a character device");
+        return Err(Box::new(io::Error::new(ErrorKind::Other, msg)));
+    }
+    let major = unsafe { libc::major(rdev) };
+    let minor = unsafe { libc::minor(rdev) };
+    Ok((major, minor))
+}