diff --git a/file_system.go b/file_system.go
index 0588966..d67fcee 100644
--- a/file_system.go
+++ b/file_system.go
@@ -57,6 +57,14 @@ type FileSystem interface {
 		ctx context.Context,
 		req *GetInodeAttributesRequest) (*GetInodeAttributesResponse, error)
 
+	// Change attributes for an inode.
+	//
+	// The kernel calls this for obvious cases like chmod(2), and for less
+	// obvious cases like ftrunctate(2).
+	SetInodeAttributes(
+		ctx context.Context,
+		req *SetInodeAttributesRequest) (*SetInodeAttributesResponse, error)
+
 	// Forget an inode ID previously issued (e.g. by LookUpInode or MkDir). The
 	// kernel calls this when removing an inode from its internal caches.
 	ForgetInode(
@@ -413,7 +421,24 @@ type GetInodeAttributesRequest struct {
 
 type GetInodeAttributesResponse struct {
 	// Attributes for the inode, and the time at which they should expire. See
-	// notes on LookUpInodeResponse.AttributesExpiration for more.
+	// notes on ChildInodeEntry.AttributesExpiration for more.
+	Attributes           InodeAttributes
+	AttributesExpiration time.Time
+}
+
+type SetInodeAttributesRequest struct {
+	Header RequestHeader
+
+	// The inode of interest.
+	Inode InodeID
+
+	// The attributes to modify, or nil for attributes that don't need a change.
+	Size *uint64
+}
+
+type SetInodeAttributesResponse struct {
+	// The new attributes for the inode, and the time at which they should
+	// expire. See notes on ChildInodeEntry.AttributesExpiration for more.
 	Attributes           InodeAttributes
 	AttributesExpiration time.Time
 }
diff --git a/fuseutil/not_implemented_file_system.go b/fuseutil/not_implemented_file_system.go
index 7cf7e2d..761723b 100644
--- a/fuseutil/not_implemented_file_system.go
+++ b/fuseutil/not_implemented_file_system.go
@@ -45,6 +45,13 @@ func (fs *NotImplementedFileSystem) GetInodeAttributes(
 	return nil, fuse.ENOSYS
 }
 
+func (fs *NotImplementedFileSystem) SetInodeAttributes(
+	ctx context.Context,
+	req *fuse.SetInodeAttributesRequest) (
+	*fuse.SetInodeAttributesResponse, error) {
+	return nil, fuse.ENOSYS
+}
+
 func (fs *NotImplementedFileSystem) ForgetInode(
 	ctx context.Context,
 	req *fuse.ForgetInodeRequest) (*fuse.ForgetInodeResponse, error) {
diff --git a/samples/memfs/fs.go b/samples/memfs/fs.go
index b65bc26..730636f 100644
--- a/samples/memfs/fs.go
+++ b/samples/memfs/fs.go
@@ -267,6 +267,32 @@ func (fs *memFS) GetInodeAttributes(
 	return
 }
 
+func (fs *memFS) SetInodeAttributes(
+	ctx context.Context,
+	req *fuse.SetInodeAttributesRequest) (
+	resp *fuse.SetInodeAttributesResponse, err error) {
+	resp = &fuse.SetInodeAttributesResponse{}
+
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+
+	// Grab the inode.
+	inode := fs.getInodeForModifyingOrDie(req.Inode)
+	defer inode.mu.Unlock()
+
+	// Handle the request.
+	inode.SetAttributes(req.Size)
+
+	// Fill in the response.
+	resp.Attributes = inode.attributes
+
+	// We don't spontaneously mutate, so the kernel can cache as long as it wants
+	// (since it also handles invalidation).
+	resp.AttributesExpiration = fs.clock.Now().Add(365 * 24 * time.Hour)
+
+	return
+}
+
 func (fs *memFS) MkDir(
 	ctx context.Context,
 	req *fuse.MkDirRequest) (resp *fuse.MkDirResponse, err error) {
diff --git a/samples/memfs/inode.go b/samples/memfs/inode.go
index 3505c13..a878fcc 100644
--- a/samples/memfs/inode.go
+++ b/samples/memfs/inode.go
@@ -369,3 +369,27 @@ func (inode *inode) WriteAt(p []byte, off int64) (n int, err error) {
 
 	return
 }
+
+// Update attributes from non-nil parameters.
+//
+// EXCLUSIVE_LOCKS_REQUIRED(inode.mu)
+func (inode *inode) SetAttributes(size *uint64) {
+	// Update the modification time.
+	inode.attributes.Mtime = inode.clock.Now()
+
+	// Truncate?
+	if size != nil {
+		intSize := int(*size)
+
+		// Update contents.
+		if intSize <= len(inode.contents) {
+			inode.contents = inode.contents[:intSize]
+		} else {
+			padding := make([]byte, intSize-len(inode.contents))
+			inode.contents = append(inode.contents, padding...)
+		}
+
+		// Update attributes.
+		inode.attributes.Size = *size
+	}
+}
diff --git a/samples/memfs/memfs_test.go b/samples/memfs/memfs_test.go
index 0fa821a..6bd4252 100644
--- a/samples/memfs/memfs_test.go
+++ b/samples/memfs/memfs_test.go
@@ -856,3 +856,98 @@ func (t *MemFSTest) ReadsPastEndOfFile() {
 	ExpectEq(0, n)
 	ExpectEq("", string(buf[:n]))
 }
+
+func (t *MemFSTest) Truncate_Smaller() {
+	var err error
+
+	fileName := path.Join(t.mfs.Dir(), "foo")
+
+	// Create a file.
+	err = ioutil.WriteFile(fileName, []byte("taco"), 0600)
+	AssertEq(nil, err)
+
+	// Open it for modification.
+	f, err := os.OpenFile(fileName, os.O_RDWR, 0)
+	t.toClose = append(t.toClose, f)
+	AssertEq(nil, err)
+
+	// Truncate it.
+	err = f.Truncate(2)
+	AssertEq(nil, err)
+
+	// Stat it.
+	fi, err := f.Stat()
+	AssertEq(nil, err)
+	ExpectEq(2, fi.Size())
+
+	// Read the contents.
+	contents, err := ioutil.ReadFile(fileName)
+	AssertEq(nil, err)
+	ExpectEq("ta", string(contents))
+}
+
+func (t *MemFSTest) Truncate_SameSize() {
+	var err error
+
+	fileName := path.Join(t.mfs.Dir(), "foo")
+
+	// Create a file.
+	err = ioutil.WriteFile(fileName, []byte("taco"), 0600)
+	AssertEq(nil, err)
+
+	// Open it for modification.
+	f, err := os.OpenFile(fileName, os.O_RDWR, 0)
+	t.toClose = append(t.toClose, f)
+	AssertEq(nil, err)
+
+	// Truncate it.
+	err = f.Truncate(4)
+	AssertEq(nil, err)
+
+	// Stat it.
+	fi, err := f.Stat()
+	AssertEq(nil, err)
+	ExpectEq(4, fi.Size())
+
+	// Read the contents.
+	contents, err := ioutil.ReadFile(fileName)
+	AssertEq(nil, err)
+	ExpectEq("taco", string(contents))
+}
+
+func (t *MemFSTest) Truncate_Larger() {
+	var err error
+
+	fileName := path.Join(t.mfs.Dir(), "foo")
+
+	// Create a file.
+	err = ioutil.WriteFile(fileName, []byte("taco"), 0600)
+	AssertEq(nil, err)
+
+	// Open it for modification.
+	f, err := os.OpenFile(fileName, os.O_RDWR, 0)
+	t.toClose = append(t.toClose, f)
+	AssertEq(nil, err)
+
+	// Truncate it.
+	err = f.Truncate(6)
+	AssertEq(nil, err)
+
+	// Stat it.
+	fi, err := f.Stat()
+	AssertEq(nil, err)
+	ExpectEq(6, fi.Size())
+
+	// Read the contents.
+	contents, err := ioutil.ReadFile(fileName)
+	AssertEq(nil, err)
+	ExpectEq("taco\x00\x00", string(contents))
+}
+
+func (t *MemFSTest) Chmod() {
+	AssertTrue(false, "TODO")
+}
+
+func (t *MemFSTest) Chtimes() {
+	AssertTrue(false, "TODO")
+}
diff --git a/server.go b/server.go
index cc343b9..811c34b 100644
--- a/server.go
+++ b/server.go
@@ -171,6 +171,34 @@ func (s *server) handleFuseRequest(fuseReq bazilfuse.Request) {
 		s.logger.Println("Responding:", fuseResp)
 		typed.Respond(fuseResp)
 
+	case *bazilfuse.SetattrRequest:
+		// Convert the request.
+		req := &SetInodeAttributesRequest{
+			Header: convertHeader(typed.Header),
+			Inode:  InodeID(typed.Header.Node),
+		}
+
+		if typed.Valid&bazilfuse.SetattrSize != 0 {
+			req.Size = &typed.Size
+		}
+
+		// Call the file system.
+		resp, err := s.fs.SetInodeAttributes(ctx, req)
+		if err != nil {
+			s.logger.Println("Responding:", err)
+			typed.RespondError(err)
+			return
+		}
+
+		// Convert the response.
+		fuseResp := &bazilfuse.SetattrResponse{
+			Attr:      convertAttributes(req.Inode, resp.Attributes),
+			AttrValid: resp.AttributesExpiration.Sub(s.clock.Now()),
+		}
+
+		s.logger.Println("Responding:", fuseResp)
+		typed.Respond(fuseResp)
+
 	case *bazilfuse.MkdirRequest:
 		// Convert the request.
 		req := &MkDirRequest{