diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index b66fca86..e48ef590 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -295,11 +295,6 @@ jobs:
           sudo apt update
           sudo apt install libpam0g-dev
 
-      - name: Rust Cache
-        uses: Swatinem/rust-cache@v2
-        with:
-          shared-key: "msrv"
-
       - name: Install rust-bindgen
         uses: taiki-e/install-action@v2
         with:
diff --git a/src/su/mod.rs b/src/su/mod.rs
index 6952640b..3f10e249 100644
--- a/src/su/mod.rs
+++ b/src/su/mod.rs
@@ -26,7 +26,7 @@ fn authenticate(
 ) -> Result<PamContext<CLIConverser>, Error> {
     let context = if login { "su-l" } else { "su" };
     let use_stdin = true;
-    let mut pam = PamContext::builder_cli("su", use_stdin, Default::default())
+    let mut pam = PamContext::builder_cli("su", use_stdin, false)
         .target_user(user)
         .service_name(context)
         .build()?;
diff --git a/src/sudo/mod.rs b/src/sudo/mod.rs
index b89b584d..faf0d450 100644
--- a/src/sudo/mod.rs
+++ b/src/sudo/mod.rs
@@ -25,7 +25,7 @@ mod pipeline;
 
 const VERSION: &str = std::env!("CARGO_PKG_VERSION");
 
-fn candidate_sudoers_file() -> &'static Path {
+pub(crate) fn candidate_sudoers_file() -> &'static Path {
     let pb_rs: &'static Path = Path::new("/etc/sudoers-rs");
     if pb_rs.exists() {
         dev_info!("Running with /etc/sudoers-rs file");
diff --git a/src/system/mod.rs b/src/system/mod.rs
index ea521f5f..5120dbcb 100644
--- a/src/system/mod.rs
+++ b/src/system/mod.rs
@@ -604,7 +604,7 @@ impl Process {
     /// attached to the given process
     pub fn tty_device_id(pid: WithProcess) -> std::io::Result<Option<DeviceId>> {
         // device id of tty is displayed as a signed integer of 32 bits
-        let data: i32 = read_proc_stat(pid, 6)?;
+        let data: i32 = read_proc_stat(pid, 6 /* tty_nr */)?;
         if data == 0 {
             Ok(None)
         } else {
@@ -619,7 +619,7 @@ impl Process {
 
     /// Get the process starting time of a specific process
     pub fn starting_time(pid: WithProcess) -> io::Result<SystemTime> {
-        let process_start: u64 = read_proc_stat(pid, 21)?;
+        let process_start: u64 = read_proc_stat(pid, 21 /* start_time */)?;
 
         // the startime field is stored in ticks since the system start, so we need to know how many
         // ticks go into a second
@@ -638,7 +638,19 @@ impl Process {
     }
 }
 
+/// Read the n-th field (with 0-based indexing) from `/proc/<pid>/self`.
+///
+/// See ["Table 1-4: Contents of the stat fields" of "The /proc
+/// Filesystem"][proc_stat_fields] in the Linux docs for all available fields.
+///
+/// IMPORTANT: the first two fields are not accessible with this routine.
+///
+/// [proc_stat_fields]: https://www.kernel.org/doc/html/latest/filesystems/proc.html#id10
 fn read_proc_stat<T: FromStr>(pid: WithProcess, field_idx: isize) -> io::Result<T> {
+    // the first two fields are skipped by the code below, and we never need them,
+    // so no point in implementing code for it in this private function.
+    debug_assert!(field_idx >= 2);
+
     // read from a specific pid file, or use `self` to refer to our own process
     let pidref = pid.to_proc_string();
 
@@ -967,4 +979,17 @@ mod tests {
         let (_, status) = child_pid.wait(WaitOptions::new()).unwrap();
         assert_eq!(status.exit_status(), Some(0));
     }
+
+    #[cfg(target_os = "linux")]
+    #[test]
+    fn proc_stat_test() {
+        use super::{read_proc_stat, Process, WithProcess::Current};
+        // the process is 'sleeping' (apparently)
+        assert_eq!("S", read_proc_stat::<String>(Current, 2).unwrap());
+        let parent = Process::parent_id().unwrap();
+        // field 3 is always the parent process
+        assert_eq!(parent, read_proc_stat::<i32>(Current, 3).unwrap());
+        // this next field should always be 0 (which precedes an important bit of info for us!)
+        assert_eq!(0, read_proc_stat::<i32>(Current, 20).unwrap());
+    }
 }
diff --git a/src/visudo/mod.rs b/src/visudo/mod.rs
index 4aec4abb..05a9f96b 100644
--- a/src/visudo/mod.rs
+++ b/src/visudo/mod.rs
@@ -11,7 +11,7 @@ use std::{
 };
 
 use crate::{
-    sudo::diagnostic,
+    sudo::{candidate_sudoers_file, diagnostic},
     sudoers::Sudoers,
     system::{
         can_execute,
@@ -64,7 +64,9 @@ pub fn main() {
 }
 
 fn check(file_arg: Option<&str>, perms: bool, owner: bool) -> io::Result<()> {
-    let sudoers_path = Path::new(file_arg.unwrap_or("/etc/sudoers"));
+    let sudoers_path = file_arg
+        .map(Path::new)
+        .unwrap_or_else(|| candidate_sudoers_file());
 
     let sudoers_file = File::open(sudoers_path)
         .map_err(|err| io_msg!(err, "unable to open {}", sudoers_path.display()))?;
@@ -121,7 +123,9 @@ fn check(file_arg: Option<&str>, perms: bool, owner: bool) -> io::Result<()> {
 }
 
 fn run(file_arg: Option<&str>, perms: bool, owner: bool) -> io::Result<()> {
-    let sudoers_path = Path::new(file_arg.unwrap_or("/etc/sudoers"));
+    let sudoers_path = file_arg
+        .map(Path::new)
+        .unwrap_or_else(|| candidate_sudoers_file());
 
     let (sudoers_file, existed) = if sudoers_path.exists() {
         let file = File::options().read(true).write(true).open(sudoers_path)?;