diff --git a/osbase/fsquota/BUILD.bazel b/osbase/fsquota/BUILD.bazel
new file mode 100644
index 0000000..350f33d
--- /dev/null
+++ b/osbase/fsquota/BUILD.bazel
@@ -0,0 +1,33 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+load("//osbase/test/ktest:ktest.bzl", "ktest")
+
+go_library(
+    name = "fsquota",
+    srcs = ["fsquota.go"],
+    importpath = "source.monogon.dev/osbase/fsquota",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//osbase/fsquota/fsxattrs",
+        "//osbase/fsquota/quotactl",
+        "@org_golang_x_sys//unix",
+    ],
+)
+
+go_test(
+    name = "fsquota_test",
+    srcs = ["fsquota_test.go"],
+    embed = [":fsquota"],
+    pure = "on",
+    deps = [
+        "@com_github_stretchr_testify//require",
+        "@org_golang_x_sys//unix",
+    ],
+)
+
+ktest(
+    cmdline = "ramdisk_size=51200",
+    files_cc = {
+        "@xfsprogs//:mkfs": "/mkfs.xfs",
+    },
+    tester = ":fsquota_test",
+)
diff --git a/osbase/fsquota/fsquota.go b/osbase/fsquota/fsquota.go
new file mode 100644
index 0000000..57acf75
--- /dev/null
+++ b/osbase/fsquota/fsquota.go
@@ -0,0 +1,143 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package fsquota provides a simplified interface to interact with Linux's
+// filesystem qouta API.  It only supports setting quotas on directories, not
+// groups or users.  Quotas need to be already enabled on the filesystem to be
+// able to use them using this package.  See the quotactl package if you intend
+// to use this on a filesystem where quotas need to be enabled manually.
+package fsquota
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"os"
+
+	"golang.org/x/sys/unix"
+
+	"source.monogon.dev/osbase/fsquota/fsxattrs"
+	"source.monogon.dev/osbase/fsquota/quotactl"
+)
+
+// SetQuota sets the quota of bytes and/or inodes in a given path. To not set a
+// limit, set the corresponding argument to zero. Setting both arguments to
+// zero removes the quota entirely.  This function can only be called on an
+// empty directory. It can't be used to create a quota below a directory which
+// already has a quota since Linux doesn't offer hierarchical quotas.
+func SetQuota(path string, maxBytes uint64, maxInodes uint64) error {
+	dir, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer dir.Close()
+	var valid uint32
+	if maxBytes > 0 {
+		valid |= quotactl.FlagBLimitsValid
+	}
+	if maxInodes > 0 {
+		valid |= quotactl.FlagILimitsValid
+	}
+
+	attrs, err := fsxattrs.Get(dir)
+	if err != nil {
+		return err
+	}
+
+	var lastID = attrs.ProjectID
+	if lastID == 0 {
+		// No project/quota exists for this directory, assign a new project
+		// quota.
+		// TODO(lorenz): This is racy, but the kernel does not support
+		// atomically assigning quotas. So this needs to be added to the
+		// kernels setquota interface. Due to the short time window and
+		// infrequent calls this should not be an immediate issue.
+		for {
+			quota, err := quotactl.GetNextQuota(dir, quotactl.QuotaTypeProject, lastID)
+			if errors.Is(err, unix.ENOENT) || errors.Is(err, unix.ESRCH) {
+				// We have enumerated all quotas, nothing exists here
+				break
+			} else if err != nil {
+				return fmt.Errorf("failed to call GetNextQuota: %w", err)
+			}
+			if quota.ID > lastID+1 {
+				// Take the first ID in the quota ID gap
+				lastID++
+				break
+			}
+			lastID++
+		}
+	}
+
+	// If both limits are zero, this is a delete operation, process it as such
+	if maxBytes == 0 && maxInodes == 0 {
+		valid = quotactl.FlagBLimitsValid | quotactl.FlagILimitsValid
+		attrs.ProjectID = 0
+		attrs.Flags &= ^fsxattrs.FlagProjectInherit
+	} else {
+		attrs.ProjectID = lastID
+		attrs.Flags |= fsxattrs.FlagProjectInherit
+	}
+
+	if err := fsxattrs.Set(dir, attrs); err != nil {
+		return err
+	}
+
+	// Always round up to the nearest block size
+	bytesLimitBlocks := uint64(math.Ceil(float64(maxBytes) / float64(1024)))
+
+	return quotactl.SetQuota(dir, quotactl.QuotaTypeProject, lastID, &quotactl.Quota{
+		BHardLimit: bytesLimitBlocks,
+		BSoftLimit: bytesLimitBlocks,
+		IHardLimit: maxInodes,
+		ISoftLimit: maxInodes,
+		Valid:      valid,
+	})
+}
+
+type Quota struct {
+	Bytes      uint64
+	BytesUsed  uint64
+	Inodes     uint64
+	InodesUsed uint64
+}
+
+// GetQuota returns the current active quota and its utilization at the given
+// path
+func GetQuota(path string) (*Quota, error) {
+	dir, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer dir.Close()
+	attrs, err := fsxattrs.Get(dir)
+	if err != nil {
+		return nil, err
+	}
+	if attrs.ProjectID == 0 {
+		return nil, os.ErrNotExist
+	}
+	quota, err := quotactl.GetQuota(dir, quotactl.QuotaTypeProject, attrs.ProjectID)
+	if err != nil {
+		return nil, err
+	}
+	return &Quota{
+		Bytes:      quota.BHardLimit * 1024,
+		BytesUsed:  quota.CurSpace,
+		Inodes:     quota.IHardLimit,
+		InodesUsed: quota.CurInodes,
+	}, nil
+}
diff --git a/osbase/fsquota/fsquota_test.go b/osbase/fsquota/fsquota_test.go
new file mode 100644
index 0000000..4044b60
--- /dev/null
+++ b/osbase/fsquota/fsquota_test.go
@@ -0,0 +1,152 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fsquota
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"os"
+	"os/exec"
+	"syscall"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/unix"
+)
+
+// withinTolerance is a helper for asserting that a value is within a certain
+// percentage of the expected value. The tolerance is specified as a float
+// between 0 (exact match) and 1 (between 0 and twice the expected value).
+func withinTolerance(t *testing.T, expected uint64, actual uint64, tolerance float64, name string) {
+	t.Helper()
+	delta := uint64(math.Round(float64(expected) * tolerance))
+	lowerBound := expected - delta
+	upperBound := expected + delta
+	if actual < lowerBound {
+		t.Errorf("Value %v (%v) is too low, expected between %v and %v", name, actual, lowerBound, upperBound)
+	}
+	if actual > upperBound {
+		t.Errorf("Value %v (%v) is too high, expected between %v and %v", name, actual, lowerBound, upperBound)
+	}
+}
+
+func TestBasic(t *testing.T) {
+	if os.Getenv("IN_KTEST") != "true" {
+		t.Skip("Not in ktest")
+	}
+	mkfsCmd := exec.Command("/mkfs.xfs", "-qf", "/dev/ram0")
+	if _, err := mkfsCmd.Output(); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Mkdir("/test", 0755); err != nil {
+		t.Error(err)
+	}
+
+	if err := unix.Mount("/dev/ram0", "/test", "xfs", unix.MS_NOEXEC|unix.MS_NODEV, "prjquota"); err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Unmount("/test", 0)
+	defer os.RemoveAll("/test")
+	t.Run("SetQuota", func(t *testing.T) {
+		defer func() {
+			os.RemoveAll("/test/set")
+		}()
+		if err := os.Mkdir("/test/set", 0755); err != nil {
+			t.Fatal(err)
+		}
+		if err := SetQuota("/test/set", 1024*1024, 100); err != nil {
+			t.Fatal(err)
+		}
+	})
+	t.Run("SetQuotaAndExhaust", func(t *testing.T) {
+		defer func() {
+			os.RemoveAll("/test/sizequota")
+		}()
+		if err := os.Mkdir("/test/sizequota", 0755); err != nil {
+			t.Fatal(err)
+		}
+		const bytesQuota = 1024 * 1024 // 1MiB
+		if err := SetQuota("/test/sizequota", bytesQuota, 0); err != nil {
+			t.Fatal(err)
+		}
+		testfile, err := os.Create("/test/sizequota/testfile")
+		if err != nil {
+			t.Fatal(err)
+		}
+		testdata := make([]byte, 1024)
+		var bytesWritten int
+		for {
+			n, err := testfile.Write(testdata)
+			if err != nil {
+				var pathErr *os.PathError
+				if errors.As(err, &pathErr) && errors.Is(pathErr.Err, syscall.ENOSPC) {
+					// Running out of space is the only acceptable error to continue execution
+					break
+				}
+				t.Fatal(err)
+			}
+			bytesWritten += n
+		}
+		if bytesWritten > bytesQuota {
+			t.Errorf("Wrote %v bytes, quota is only %v bytes", bytesWritten, bytesQuota)
+		}
+	})
+	t.Run("GetQuotaReadbackAndUtilization", func(t *testing.T) {
+		defer func() {
+			os.RemoveAll("/test/readback")
+		}()
+		if err := os.Mkdir("/test/readback", 0755); err != nil {
+			t.Fatal(err)
+		}
+		const bytesQuota = 1024 * 1024 // 1MiB
+		const inodesQuota = 100
+		if err := SetQuota("/test/readback", bytesQuota, inodesQuota); err != nil {
+			t.Fatal(err)
+		}
+		sizeFileData := make([]byte, 512*1024)
+		if err := os.WriteFile("/test/readback/512kfile", sizeFileData, 0644); err != nil {
+			t.Fatal(err)
+		}
+
+		quotaUtil, err := GetQuota("/test/readback")
+		if err != nil {
+			t.Fatal(err)
+		}
+		require.Equal(t, uint64(bytesQuota), quotaUtil.Bytes, "bytes quota readback incorrect")
+		require.Equal(t, uint64(inodesQuota), quotaUtil.Inodes, "inodes quota readback incorrect")
+
+		// Give 10% tolerance for quota used values to account for metadata
+		// overhead and internal structures that are also in there. If it's out
+		// by more than that it's an issue anyways.
+		withinTolerance(t, uint64(len(sizeFileData)), quotaUtil.BytesUsed, 0.1, "BytesUsed")
+
+		// Write 50 inodes for a total of 51 (with the 512K file)
+		for i := 0; i < 50; i++ {
+			if err := os.WriteFile(fmt.Sprintf("/test/readback/ifile%v", i), []byte("test"), 0644); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		quotaUtil, err = GetQuota("/test/readback")
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		withinTolerance(t, 51, quotaUtil.InodesUsed, 0.1, "InodesUsed")
+	})
+}
diff --git a/osbase/fsquota/fsxattrs/BUILD.bazel b/osbase/fsquota/fsxattrs/BUILD.bazel
new file mode 100644
index 0000000..b5217aa
--- /dev/null
+++ b/osbase/fsquota/fsxattrs/BUILD.bazel
@@ -0,0 +1,9 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "fsxattrs",
+    srcs = ["fsxattrs.go"],
+    importpath = "source.monogon.dev/osbase/fsquota/fsxattrs",
+    visibility = ["//visibility:public"],
+    deps = ["@org_golang_x_sys//unix"],
+)
diff --git a/osbase/fsquota/fsxattrs/fsxattrs.go b/osbase/fsquota/fsxattrs/fsxattrs.go
new file mode 100644
index 0000000..135b886
--- /dev/null
+++ b/osbase/fsquota/fsxattrs/fsxattrs.go
@@ -0,0 +1,81 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fsxattrs
+
+import (
+	"fmt"
+	"os"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+type FSXAttrFlag uint32
+
+// Defined in uapi/linux/fs.h
+const (
+	FlagRealtime        FSXAttrFlag = 0x00000001
+	FlagPreallocated    FSXAttrFlag = 0x00000002
+	FlagImmutable       FSXAttrFlag = 0x00000008
+	FlagAppend          FSXAttrFlag = 0x00000010
+	FlagSync            FSXAttrFlag = 0x00000020
+	FlagNoATime         FSXAttrFlag = 0x00000040
+	FlagNoDump          FSXAttrFlag = 0x00000080
+	FlagRealtimeInherit FSXAttrFlag = 0x00000100
+	FlagProjectInherit  FSXAttrFlag = 0x00000200
+	FlagNoSymlinks      FSXAttrFlag = 0x00000400
+	FlagExtentSize      FSXAttrFlag = 0x00000800
+	FlagNoDefragment    FSXAttrFlag = 0x00002000
+	FlagFilestream      FSXAttrFlag = 0x00004000
+	FlagDAX             FSXAttrFlag = 0x00008000
+	FlagCOWExtentSize   FSXAttrFlag = 0x00010000
+	FlagHasAttribute    FSXAttrFlag = 0x80000000
+)
+
+// FS_IOC_FSGETXATTR and FS_IOC_FSSETXATTR are defined in uapi/linux/fs.h
+// and normally would be imported from x/sys/unix. Since they don't exist
+// there define them here for now.
+const (
+	FS_IOC_FSGETXATTR = 0x801c581f
+	FS_IOC_FSSETXATTR = 0x401c5820
+)
+
+type FSXAttrs struct {
+	Flags         FSXAttrFlag
+	ExtentSize    uint32
+	ExtentCount   uint32
+	ProjectID     uint32
+	CoWExtentSize uint32
+	_pad          [8]byte
+}
+
+func Get(file *os.File) (*FSXAttrs, error) {
+	var attrs FSXAttrs
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL, file.Fd(), FS_IOC_FSGETXATTR, uintptr(unsafe.Pointer(&attrs)))
+	if errno != 0 {
+		return nil, fmt.Errorf("failed to execute getFSXAttrs: %v", errno)
+	}
+	return &attrs, nil
+}
+
+func Set(file *os.File, attrs *FSXAttrs) error {
+	_, _, errno := unix.Syscall(unix.SYS_IOCTL, file.Fd(), FS_IOC_FSSETXATTR, uintptr(unsafe.Pointer(attrs)))
+	if errno != 0 {
+		return fmt.Errorf("failed to execute setFSXAttrs: %v", errno)
+	}
+	return nil
+}
diff --git a/osbase/fsquota/quotactl/BUILD.bazel b/osbase/fsquota/quotactl/BUILD.bazel
new file mode 100644
index 0000000..57995fe
--- /dev/null
+++ b/osbase/fsquota/quotactl/BUILD.bazel
@@ -0,0 +1,9 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "quotactl",
+    srcs = ["quotactl.go"],
+    importpath = "source.monogon.dev/osbase/fsquota/quotactl",
+    visibility = ["//visibility:public"],
+    deps = ["@org_golang_x_sys//unix"],
+)
diff --git a/osbase/fsquota/quotactl/quotactl.go b/osbase/fsquota/quotactl/quotactl.go
new file mode 100644
index 0000000..c7939ed
--- /dev/null
+++ b/osbase/fsquota/quotactl/quotactl.go
@@ -0,0 +1,199 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package quotactl implements a low-level wrapper around the modern portion of
+// Linux's quotactl() syscall. See the fsquota package for a nicer interface to
+// the most common part of this API.
+package quotactl
+
+import (
+	"fmt"
+	"os"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+type QuotaType uint
+
+const (
+	QuotaTypeUser QuotaType = iota
+	QuotaTypeGroup
+	QuotaTypeProject
+)
+
+const (
+	Q_SYNC uint = (0x800001 + iota) << 8
+	Q_QUOTAON
+	Q_QUOTAOFF
+	Q_GETFMT
+	Q_GETINFO
+	Q_SETINFO
+	Q_GETQUOTA
+	Q_SETQUOTA
+	Q_GETNEXTQUOTA
+)
+
+const (
+	FlagBLimitsValid = 1 << iota
+	FlagSpaceValid
+	FlagILimitsValid
+	FlagInodesValid
+	FlagBTimeValid
+	FlagITimeValid
+)
+
+type DQInfo struct {
+	Bgrace uint64
+	Igrace uint64
+	Flags  uint32
+	Valid  uint32
+}
+
+type Quota struct {
+	BHardLimit uint64 // Both Byte limits are prescaled by 1024 (so are in KiB), but CurSpace is in B
+	BSoftLimit uint64
+	CurSpace   uint64
+	IHardLimit uint64
+	ISoftLimit uint64
+	CurInodes  uint64
+	BTime      uint64
+	ITime      uint64
+	Valid      uint32
+}
+
+type NextDQBlk struct {
+	HardLimitBytes  uint64
+	SoftLimitBytes  uint64
+	CurrentBytes    uint64
+	HardLimitInodes uint64
+	SoftLimitInodes uint64
+	CurrentInodes   uint64
+	BTime           uint64
+	ITime           uint64
+	Valid           uint32
+	ID              uint32
+}
+
+type QuotaFormat uint32
+
+// Collected from quota_format_type structs
+const (
+	// QuotaFormatNone is a special case where all quota information is
+	// stored inside filesystem metadata and thus requires no quotaFilePath.
+	QuotaFormatNone   QuotaFormat = 0
+	QuotaFormatVFSOld QuotaFormat = 1
+	QuotaFormatVFSV0  QuotaFormat = 2
+	QuotaFormatOCFS2  QuotaFormat = 3
+	QuotaFormatVFSV1  QuotaFormat = 4
+)
+
+// QuotaOn turns quota accounting and enforcement on
+func QuotaOn(fd *os.File, qtype QuotaType, quotaFormat QuotaFormat, quotaFilePath string) error {
+	pathArg, err := unix.BytePtrFromString(quotaFilePath)
+	if err != nil {
+		return err
+	}
+	_, _, errNo := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_QUOTAON|uint(qtype)), uintptr(quotaFormat), uintptr(unsafe.Pointer(pathArg)), 0, 0)
+	if errNo != unix.Errno(0) {
+		return errNo
+	}
+	return nil
+}
+
+// QuotaOff turns quotas off
+func QuotaOff(fd *os.File, qtype QuotaType) error {
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_QUOTAOFF|uint(qtype)), 0, 0, 0, 0)
+	if err != unix.Errno(0) {
+		return err
+	}
+	return nil
+}
+
+// GetFmt gets the quota format used on given filesystem
+func GetFmt(fd *os.File, qtype QuotaType) (QuotaFormat, error) {
+	var fmt uint32
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_GETFMT|uint(qtype)), 0, uintptr(unsafe.Pointer(&fmt)), 0, 0)
+	if err != unix.Errno(0) {
+		return 0, err
+	}
+	return QuotaFormat(fmt), nil
+}
+
+// GetInfo gets information about quota files
+func GetInfo(fd *os.File, qtype QuotaType) (*DQInfo, error) {
+	var info DQInfo
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_GETINFO|uint(qtype)), 0, uintptr(unsafe.Pointer(&info)), 0, 0)
+	if err != unix.Errno(0) {
+		return nil, err
+	}
+	return &info, nil
+}
+
+// SetInfo sets information about quota files
+func SetInfo(fd *os.File, qtype QuotaType, info *DQInfo) error {
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_SETINFO|uint(qtype)), 0, uintptr(unsafe.Pointer(info)), 0, 0)
+	if err != unix.Errno(0) {
+		return err
+	}
+	return nil
+}
+
+// GetQuota gets user quota structure
+func GetQuota(fd *os.File, qtype QuotaType, id uint32) (*Quota, error) {
+	var info Quota
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_GETQUOTA|uint(qtype)), uintptr(id), uintptr(unsafe.Pointer(&info)), 0, 0)
+	if err != unix.Errno(0) {
+		return nil, err
+	}
+	return &info, nil
+}
+
+// GetNextQuota gets disk limits and usage > ID
+func GetNextQuota(fd *os.File, qtype QuotaType, id uint32) (*NextDQBlk, error) {
+	var info NextDQBlk
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_GETNEXTQUOTA|uint(qtype)), uintptr(id), uintptr(unsafe.Pointer(&info)), 0, 0)
+	if err != unix.Errno(0) {
+		return nil, err
+	}
+	return &info, nil
+}
+
+// SetQuota sets the given quota
+func SetQuota(fd *os.File, qtype QuotaType, id uint32, quota *Quota) error {
+	_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_SETQUOTA|uint(qtype)), uintptr(id), uintptr(unsafe.Pointer(quota)), 0, 0)
+	if err != unix.Errno(0) {
+		return fmt.Errorf("failed to set quota: %w", err)
+	}
+	return nil
+}
+
+// Sync syncs disk copy of filesystems quotas. If device is empty it syncs all
+// filesystems.
+func Sync(fd *os.File) error {
+	if fd != nil {
+		_, _, err := unix.Syscall6(unix.SYS_QUOTACTL_FD, fd.Fd(), uintptr(Q_SYNC), 0, 0, 0, 0)
+		if err != unix.Errno(0) {
+			return err
+		}
+	} else {
+		_, _, err := unix.Syscall6(unix.SYS_QUOTACTL, uintptr(Q_SYNC), 0, 0, 0, 0, 0)
+		if err != unix.Errno(0) {
+			return err
+		}
+	}
+	return nil
+}