diff --git a/src/header/unistd/mod.rs b/src/header/unistd/mod.rs
--- a/src/header/unistd/mod.rs
+++ b/src/header/unistd/mod.rs
@@ -537,8 +537,39 @@
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getentropy.html>.
 // #[unsafe(no_mangle)]
-pub extern "C" fn getentropy(buffer: *mut c_void, length: size_t) -> c_int {
-    unimplemented!();
+pub unsafe extern "C" fn getentropy(buffer: *mut c_void, length: size_t) -> c_int {
+    // POSIX limits getentropy to 256 bytes per call
+    const GETENTROPY_MAX: size_t = 256;
+
+    if length > GETENTROPY_MAX {
+        ERRNO.set(EINVAL);
+        return -1;
+    }
+
+    let path = unsafe { CStr::from_ptr(c"/scheme/rand".as_ptr().cast()) };
+    let fd = match Sys::open(path, fcntl::O_RDONLY, 0) {
+        Ok(fd) => fd,
+        Err(Errno(e)) => {
+            ERRNO.set(e);
+            return -1;
+        }
+    };
+
+    let buf = unsafe { slice::from_raw_parts_mut(buffer.cast::<u8>(), length) };
+    let mut filled = 0usize;
+    while filled < length {
+        match Sys::read(fd, &mut buf[filled..]) {
+            Ok(0) => break,
+            Ok(n) => filled += n,
+            Err(Errno(e)) => {
+                let _ = Sys::close(fd);
+                ERRNO.set(e);
+                return -1;
+            }
+        }
+    }
+    let _ = Sys::close(fd);
+    if filled < length { ERRNO.set(errno::EIO); -1 } else { 0 }
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/geteuid.html>.