diff --git a/src/scheme/proc.rs b/src/scheme/proc.rs
index c9c8fea3f9..d8abeea4af 100644
--- a/src/scheme/proc.rs
+++ b/src/scheme/proc.rs
@@ -771,25 +771,59 @@ impl KernelScheme for ProcScheme {
                 } => {
                     // TODO: Maybe allow userspace to either copy or transfer recently dupped file
                     // descriptors between file tables.
-                    if buf != b"copy" {
-                        return Err(Error::new(EINVAL));
-                    }
-                    let filetable = filetable.upgrade().ok_or(Error::new(EOWNERDEAD))?;
+                    let new_handle = match buf {
+                        b"copy" => {
+                            let filetable = filetable.upgrade().ok_or(Error::new(EOWNERDEAD))?;
 
-                    let new_filetable =
-                        Arc::new(RwLock::new(filetable.read(token.token()).clone()));
+                            let new_filetable =
+                                Arc::new(RwLock::new(filetable.read(token.token()).clone()));
 
-                    handle(
-                        Handle {
-                            kind: ContextHandle::NewFiletable {
-                                filetable: new_filetable,
-                                binary_format,
-                                data: data.clone(),
-                            },
-                            context,
-                        },
-                        true,
-                    )
+                            Handle {
+                                kind: ContextHandle::NewFiletable {
+                                    filetable: new_filetable,
+                                    binary_format,
+                                    data: data.clone(),
+                                },
+                                context,
+                            }
+                        }
+                        b"refresh" => {
+                            let filetable = filetable.upgrade().ok_or(Error::new(EOWNERDEAD))?;
+
+                            let new_data = if binary_format {
+                                let mut data = Vec::new();
+                                for index in filetable
+                                    .read(token.token())
+                                    .enumerate()
+                                    .filter_map(|(idx, val)| val.as_ref().map(|_| idx))
+                                {
+                                    data.extend((index as u64).to_le_bytes());
+                                }
+                                data.into_boxed_slice()
+                            } else {
+                                use core::fmt::Write;
+                                let mut data = String::new();
+                                for index in filetable
+                                    .read(token.token())
+                                    .enumerate()
+                                    .filter_map(|(idx, val)| val.as_ref().map(|_| idx))
+                                {
+                                    writeln!(data, "{}", index).unwrap();
+                                }
+                                data.into_bytes().into_boxed_slice()
+                            };
+                            Handle {
+                                kind: ContextHandle::Filetable {
+                                    filetable: Arc::downgrade(&filetable),
+                                    binary_format,
+                                    data: new_data,
+                                },
+                                context,
+                            }
+                        }
+                        _ => return Err(Error::new(EINVAL)),
+                    };
+                    handle(new_handle, true)
                 }
                 Handle {
                     kind: ContextHandle::AddrSpace { ref addrspace },
diff --git a/src/syscall/fs.rs b/src/syscall/fs.rs
index f796517c2e..35d6a49e4e 100644
--- a/src/syscall/fs.rs
+++ b/src/syscall/fs.rs
@@ -235,19 +235,36 @@ pub fn dup2(
     buf: UserSliceRo,
     token: &mut CleanLockToken,
 ) -> Result<FileHandle> {
-    if fd == new_fd {
-        Ok(new_fd)
-    } else {
-        let _ = close(new_fd, token);
-        let new_file = duplicate_file(fd, buf, token)?;
-
-        let current_lock = context::current();
-        let mut current = current_lock.read(token.token());
-        let (context, mut token) = current.token_split();
-        context
-            .insert_file(new_fd, new_file, &mut token)
-            .ok_or(Error::new(EMFILE))
+    if fd == new_fd && buf.is_empty() {
+        return Ok(new_fd);
     }
+
+    let new_file = duplicate_file(fd, buf, token)?;
+
+    let old_file = {
+        let current_lock = context::current();
+        let mut current = current_lock.write(token.token());
+        let (context, mut split_token) = current.token_split();
+
+        let old_file = context.remove_file(new_fd, &mut split_token.token());
+
+        if context
+            .insert_file(new_fd, new_file, &mut split_token.token())
+            .is_none()
+        {
+            if let Some(old) = old_file {
+                context.insert_file(new_fd, old, &mut split_token.token());
+            }
+            return Err(Error::new(EMFILE));
+        }
+        old_file
+    };
+
+    if let Some(old) = old_file {
+        let _ = old.close(token);
+    }
+
+    Ok(new_fd)
 }
 pub fn call(
     fds: &[usize],