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+---
+title: Known Environment Variables
+category: Interfaces
+layout: default
+SPDX-License-Identifier: LGPL-2.1-or-later
+---
+
+# Known Environment Variables
+
+A number of systemd components take additional runtime parameters via
+environment variables. Many of these environment variables are not supported at
+the same level as command line switches and other interfaces are: we don't
+document them in the man pages and we make no stability guarantees for
+them. While they generally are unlikely to be dropped any time soon again, we
+do not want to guarantee that they stay around for good either.
+
+Below is an (incomprehensive) list of the environment variables understood by
+the various tools. Note that this list only covers environment variables not
+documented in the proper man pages.
+
+All tools:
+
+* `$SYSTEMD_OFFLINE=[0|1]` — if set to `1`, then `systemctl` will refrain from
+ talking to PID 1; this has the same effect as the historical detection of
+ `chroot()`. Setting this variable to `0` instead has a similar effect as
+ `$SYSTEMD_IGNORE_CHROOT=1`; i.e. tools will try to communicate with PID 1
+ even if a `chroot()` environment is detected. You almost certainly want to
+ set this to `1` if you maintain a package build system or similar and are
+ trying to use a modern container system and not plain `chroot()`.
+
+* `$SYSTEMD_IGNORE_CHROOT=1` — if set, don't check whether being invoked in a
+ `chroot()` environment. This is particularly relevant for systemctl, as it
+ will not alter its behaviour for `chroot()` environments if set. Normally it
+ refrains from talking to PID 1 in such a case; turning most operations such
+ as `start` into no-ops. If that's what's explicitly desired, you might
+ consider setting `$SYSTEMD_OFFLINE=1`.
+
+* `$SD_EVENT_PROFILE_DELAYS=1` — if set, the sd-event event loop implementation
+ will print latency information at runtime.
+
+* `$SYSTEMD_PROC_CMDLINE` — if set, the contents are used as the kernel command
+ line instead of the actual one in `/proc/cmdline`. This is useful for
+ debugging, in order to test generators and other code against specific kernel
+ command lines.
+
+* `$SYSTEMD_OS_RELEASE` — if set, use this path instead of `/etc/os-release` or
+ `/usr/lib/os-release`. When operating under some root (e.g. `systemctl
+ --root=…`), the path is taken relative to the outside root. Only useful for
+ debugging.
+
+* `$SYSTEMD_FSTAB` — if set, use this path instead of `/etc/fstab`. Only useful
+ for debugging.
+
+* `$SYSTEMD_SYSROOT_FSTAB` — if set, use this path instead of
+ `/sysroot/etc/fstab`. Only useful for debugging `systemd-fstab-generator`.
+
+* `$SYSTEMD_CRYPTTAB` — if set, use this path instead of `/etc/crypttab`. Only
+ useful for debugging. Currently only supported by
+ `systemd-cryptsetup-generator`.
+
+* `$SYSTEMD_INTEGRITYTAB` — if set, use this path instead of
+ `/etc/integritytab`. Only useful for debugging. Currently only supported by
+ `systemd-integritysetup-generator`.
+
+* `$SYSTEMD_VERITYTAB` — if set, use this path instead of
+ `/etc/veritytab`. Only useful for debugging. Currently only supported by
+ `systemd-veritysetup-generator`.
+
+* `$SYSTEMD_EFI_OPTIONS` — if set, used instead of the string in the
+ `SystemdOptions` EFI variable. Analogous to `$SYSTEMD_PROC_CMDLINE`.
+
+* `$SYSTEMD_DEFAULT_HOSTNAME` — override the compiled-in fallback hostname
+ (relevant in particular for the system manager and `systemd-hostnamed`).
+ Must be a valid hostname (either a single label or a FQDN).
+
+* `$SYSTEMD_IN_INITRD` — takes a boolean. If set, overrides initrd detection.
+ This is useful for debugging and testing initrd-only programs in the main
+ system.
+
+* `$SYSTEMD_BUS_TIMEOUT=SECS` — specifies the maximum time to wait for method call
+ completion. If no time unit is specified, assumes seconds. The usual other units
+ are understood, too (us, ms, s, min, h, d, w, month, y). If it is not set or set
+ to 0, then the built-in default is used.
+
+* `$SYSTEMD_MEMPOOL=0` — if set, the internal memory caching logic employed by
+ hash tables is turned off, and libc `malloc()` is used for all allocations.
+
+* `$SYSTEMD_EMOJI=0` — if set, tools such as `systemd-analyze security` will
+ not output graphical smiley emojis, but ASCII alternatives instead. Note that
+ this only controls use of Unicode emoji glyphs, and has no effect on other
+ Unicode glyphs.
+
+* `$RUNTIME_DIRECTORY` — various tools use this variable to locate the
+ appropriate path under `/run/`. This variable is also set by the manager when
+ `RuntimeDirectory=` is used, see systemd.exec(5).
+
+* `$SYSTEMD_CRYPT_PREFIX` — if set configures the hash method prefix to use for
+ UNIX `crypt()` when generating passwords. By default the system's "preferred
+ method" is used, but this can be overridden with this environment variable.
+ Takes a prefix such as `$6$` or `$y$`. (Note that this is only honoured on
+ systems built with libxcrypt and is ignored on systems using glibc's
+ original, internal `crypt()` implementation.)
+
+* `$SYSTEMD_SECCOMP=0` — if set, seccomp filters will not be enforced, even if
+ support for it is compiled in and available in the kernel.
+
+* `$SYSTEMD_LOG_SECCOMP=1` — if set, system calls blocked by seccomp filtering,
+ for example in `systemd-nspawn`, will be logged to the audit log, if the
+ kernel supports this.
+
+`systemctl`:
+
+* `$SYSTEMCTL_FORCE_BUS=1` — if set, do not connect to PID 1's private D-Bus
+ listener, and instead always connect through the dbus-daemon D-bus broker.
+
+* `$SYSTEMCTL_INSTALL_CLIENT_SIDE=1` — if set, enable or disable unit files on
+ the client side, instead of asking PID 1 to do this.
+
+* `$SYSTEMCTL_SKIP_SYSV=1` — if set, do not call SysV compatibility hooks.
+
+`systemd-nspawn`:
+
+* `$SYSTEMD_NSPAWN_UNIFIED_HIERARCHY=1` — if set, force `systemd-nspawn` into
+ unified cgroup hierarchy mode.
+
+* `$SYSTEMD_NSPAWN_API_VFS_WRITABLE=1` — if set, make `/sys/`, `/proc/sys/`,
+ and friends writable in the container. If set to "network", leave only
+ `/proc/sys/net/` writable.
+
+* `$SYSTEMD_NSPAWN_CONTAINER_SERVICE=…` — override the "service" name nspawn
+ uses to register with machined. If unset defaults to "nspawn", but with this
+ variable may be set to any other value.
+
+* `$SYSTEMD_NSPAWN_USE_CGNS=0` — if set, do not use cgroup namespacing, even if
+ it is available.
+
+* `$SYSTEMD_NSPAWN_LOCK=0` — if set, do not lock container images when running.
+
+* `$SYSTEMD_NSPAWN_TMPFS_TMP=0` — if set, do not overmount `/tmp/` in the
+ container with a tmpfs, but leave the directory from the image in place.
+
+* `$SYSTEMD_SUPPRESS_SYNC=1` — if set, all disk synchronization syscalls are
+ blocked to the container payload (e.g. `sync()`, `fsync()`, `syncfs()`, …)
+ and the `O_SYNC`/`O_DSYNC` flags are made unavailable to `open()` and
+ friends. This is equivalent to passing `--suppress-sync=yes` on the
+ `systemd-nspawn` command line.
+
+`systemd-logind`:
+
+* `$SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK=1` — if set, report that
+ hibernation is available even if the swap devices do not provide enough room
+ for it.
+
+* `$SYSTEMD_REBOOT_TO_FIRMWARE_SETUP` — if set, overrides `systemd-logind`'s
+ built-in EFI logic of requesting a reboot into the firmware. Takes a boolean.
+ If set to false, the functionality is turned off entirely. If set to true,
+ instead of requesting a reboot into the firmware setup UI through EFI a file,
+ `/run/systemd/reboot-to-firmware-setup` is created whenever this is
+ requested. This file may be checked for by services run during system
+ shutdown in order to request the appropriate operation from the firmware in
+ an alternative fashion.
+
+* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_MENU` — similar to the above, allows
+ overriding of `systemd-logind`'s built-in EFI logic of requesting a reboot
+ into the boot loader menu. Takes a boolean. If set to false, the
+ functionality is turned off entirely. If set to true, instead of requesting a
+ reboot into the boot loader menu through EFI, the file
+ `/run/systemd/reboot-to-boot-loader-menu` is created whenever this is
+ requested. The file contains the requested boot loader menu timeout in µs,
+ formatted in ASCII decimals, or zero in case no timeout is requested. This
+ file may be checked for by services run during system shutdown in order to
+ request the appropriate operation from the boot loader in an alternative
+ fashion.
+
+* `$SYSTEMD_REBOOT_TO_BOOT_LOADER_ENTRY` — similar to the above, allows
+ overriding of `systemd-logind`'s built-in EFI logic of requesting a reboot
+ into a specific boot loader entry. Takes a boolean. If set to false, the
+ functionality is turned off entirely. If set to true, instead of requesting a
+ reboot into a specific boot loader entry through EFI, the file
+ `/run/systemd/reboot-to-boot-loader-entry` is created whenever this is
+ requested. The file contains the requested boot loader entry identifier. This
+ file may be checked for by services run during system shutdown in order to
+ request the appropriate operation from the boot loader in an alternative
+ fashion. Note that by default only boot loader entries which follow the
+ [Boot Loader Specification](BOOT_LOADER_SPECIFICATION.md) and are
+ placed in the ESP or the Extended Boot Loader partition may be selected this
+ way. However, if a directory `/run/boot-loader-entries/` exists, the entries
+ are loaded from there instead. The directory should contain the usual
+ directory hierarchy mandated by the Boot Loader Specification, i.e. the entry
+ drop-ins should be placed in
+ `/run/boot-loader-entries/loader/entries/*.conf`, and the files referenced by
+ the drop-ins (including the kernels and initrds) somewhere else below
+ `/run/boot-loader-entries/`. Note that all these files may be (and are
+ supposed to be) symlinks. `systemd-logind` will load these files on-demand,
+ these files can hence be updated (ideally atomically) whenever the boot
+ loader configuration changes. A foreign boot loader installer script should
+ hence synthesize drop-in snippets and symlinks for all boot entries at boot
+ or whenever they change if it wants to integrate with `systemd-logind`'s
+ APIs.
+
+`systemd-udevd` and sd-device library:
+
+* `$NET_NAMING_SCHEME=` — if set, takes a network naming scheme (i.e. one of
+ "v238", "v239", "v240"…, or the special value "latest") as parameter. If
+ specified udev's `net_id` builtin will follow the specified naming scheme
+ when determining stable network interface names. This may be used to revert
+ to naming schemes of older udev versions, in order to provide more stable
+ naming across updates. This environment variable takes precedence over the
+ kernel command line option `net.naming-scheme=`, except if the value is
+ prefixed with `:` in which case the kernel command line option takes
+ precedence, if it is specified as well.
+
+* `$SYSTEMD_DEVICE_VERIFY_SYSFS` — if set to "0", disables verification that
+ devices sysfs path are actually backed by sysfs. Relaxing this verification
+ is useful for testing purposes.
+
+`nss-systemd`:
+
+* `$SYSTEMD_NSS_BYPASS_SYNTHETIC=1` — if set, `nss-systemd` won't synthesize
+ user/group records for the `root` and `nobody` users if they are missing from
+ `/etc/passwd`.
+
+* `$SYSTEMD_NSS_DYNAMIC_BYPASS=1` — if set, `nss-systemd` won't return
+ user/group records for dynamically registered service users (i.e. users
+ registered through `DynamicUser=1`).
+
+`systemd-timedated`:
+
+* `$SYSTEMD_TIMEDATED_NTP_SERVICES=…` — colon-separated list of unit names of
+ NTP client services. If set, `timedatectl set-ntp on` enables and starts the
+ first existing unit listed in the environment variable, and
+ `timedatectl set-ntp off` disables and stops all listed units.
+
+`systemd-sulogin-shell`:
+
+* `$SYSTEMD_SULOGIN_FORCE=1` — This skips asking for the root password if the
+ root password is not available (such as when the root account is locked).
+ See `sulogin(8)` for more details.
+
+`bootctl` and other tools that access the EFI System Partition (ESP):
+
+* `$SYSTEMD_RELAX_ESP_CHECKS=1` — if set, the ESP validation checks are
+ relaxed. Specifically, validation checks that ensure the specified ESP path
+ is a FAT file system are turned off, as are checks that the path is located
+ on a GPT partition with the correct type UUID.
+
+* `$SYSTEMD_ESP_PATH=…` — override the path to the EFI System Partition. This
+ may be used to override ESP path auto detection, and redirect any accesses to
+ the ESP to the specified directory. Note that unlike with `bootctl`'s
+ `--path=` switch only very superficial validation of the specified path is
+ done when this environment variable is used.
+
+`systemd` itself:
+
+* `$SYSTEMD_ACTIVATION_UNIT` — set for all NSS and PAM module invocations that
+ are done by the service manager on behalf of a specific unit, in child
+ processes that are later (after execve()) going to become unit
+ processes. Contains the full unit name (e.g. "foobar.service"). NSS and PAM
+ modules can use this information to determine in which context and on whose
+ behalf they are being called, which may be useful to avoid deadlocks, for
+ example to bypass IPC calls to the very service that is about to be
+ started. Note that NSS and PAM modules should be careful to only rely on this
+ data when invoked privileged, or possibly only when getppid() returns 1, as
+ setting environment variables is of course possible in any even unprivileged
+ contexts.
+
+* `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
+ it is either set to `system` or `user` depending on whether the NSS/PAM
+ module is called by systemd in `--system` or `--user` mode.
+
+* `$SYSTEMD_DEFAULT_MOUNT_RATE_LIMIT_BURST` — can be set to override the mount
+ units burst rate limit for parsing `/proc/self/mountinfo`. On a system with
+ few resources but many mounts the rate limit may be hit, which will cause the
+ processing of mount units to stall. The burst limit may be adjusted when the
+ default is not appropriate for a given system. Defaults to `5`, accepts
+ positive integers.
+
+`systemd-remount-fs`:
+
+* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and no entry for the root directory
+ exists in `/etc/fstab` (this file always takes precedence), then the root
+ directory is remounted writable. This is primarily used by
+ `systemd-gpt-auto-generator` to ensure the root partition is mounted writable
+ in accordance to the GPT partition flags.
+
+`systemd-firstboot` and `localectl`:
+
+* `$SYSTEMD_LIST_NON_UTF8_LOCALES=1` — if set, non-UTF-8 locales are listed among
+ the installed ones. By default non-UTF-8 locales are suppressed from the
+ selection, since we are living in the 21st century.
+
+`systemd-resolved`:
+
+* `$SYSTEMD_RESOLVED_SYNTHESIZE_HOSTNAME` — if set to "0", `systemd-resolved`
+ won't synthesize system hostname on both regular and reverse lookups.
+
+`systemd-sysext`:
+
+* `$SYSTEMD_SYSEXT_HIERARCHIES` — this variable may be used to override which
+ hierarchies are managed by `systemd-sysext`. By default only `/usr/` and
+ `/opt/` are managed, and directories may be added or removed to that list by
+ setting this environment variable to a colon-separated list of absolute
+ paths. Only "real" file systems and directories that only contain "real" file
+ systems as submounts should be used. Do not specify API file systems such as
+ `/proc/` or `/sys/` here, or hierarchies that have them as submounts. In
+ particular, do not specify the root directory `/` here.
+
+`systemd-tmpfiles`:
+
+* `$SYSTEMD_TMPFILES_FORCE_SUBVOL` — if unset, `v`/`q`/`Q` lines will create
+ subvolumes only if the OS itself is installed into a subvolume. If set to `1`
+ (or another value interpreted as true), these lines will always create
+ subvolumes if the backing filesystem supports them. If set to `0`, these
+ lines will always create directories.
+
+`systemd-sysusers`
+
+* `SOURCE_DATE_EPOCH` — if unset, the field of the date of last password change
+ in `/etc/shadow` will be the number of days from Jan 1, 1970 00:00 UTC until
+ today. If SOURCE_DATE_EPOCH is set to a valid UNIX epoch value in seconds,
+ then the field will be the number of days until that time instead. This is to
+ support creating bit-by-bit reproducible system images by choosing a
+ reproducible value for the field of the date of last password change in
+ `/etc/shadow`. See: https://reproducible-builds.org/specs/source-date-epoch/
+
+`systemd-sysv-generator`:
+
+* `$SYSTEMD_SYSVINIT_PATH` — Controls where `systemd-sysv-generator` looks for
+ SysV init scripts.
+
+* `$SYSTEMD_SYSVRCND_PATH` — Controls where `systemd-sysv-generator` looks for
+ SysV init script runlevel link farms.
+
+systemd tests:
+
+* `$SYSTEMD_TEST_DATA` — override the location of test data. This is useful if
+ a test executable is moved to an arbitrary location.
+
+* `$SYSTEMD_TEST_NSS_BUFSIZE` — size of scratch buffers for "reentrant"
+ functions exported by the nss modules.
+
+fuzzers:
+
+* `$SYSTEMD_FUZZ_OUTPUT` — A boolean that specifies whether to write output to
+ stdout. Setting to true is useful in manual invocations, since all output is
+ suppressed by default.
+
+* `$SYSTEMD_FUZZ_RUNS` — The number of times execution should be repeated in
+ manual invocations.
+
+Note that it may be also useful to set `$SYSTEMD_LOG_LEVEL`, since all logging
+is suppressed by default.
+
+`systemd-importd`:
+
+* `$SYSTEMD_IMPORT_BTRFS_SUBVOL` — takes a boolean, which controls whether to
+ prefer creating btrfs subvolumes over plain directories for machine
+ images. Has no effect on non-btrfs file systems where subvolumes are not
+ available anyway. If not set, defaults to true.
+
+* `$SYSTEMD_IMPORT_BTRFS_QUOTA` — takes a boolean, which controls whether to set
+ up quota automatically for created btrfs subvolumes for machine images. If
+ not set, defaults to true. Has no effect if machines are placed in regular
+ directories, because btrfs subvolumes are not supported or disabled. If
+ enabled, the quota group of the subvolume is automatically added to a
+ combined quota group for all such machine subvolumes.
+
+* `$SYSTEMD_IMPORT_SYNC` — takes a boolean, which controls whether to
+ synchronize images to disk after installing them, before completing the
+ operation. If not set, defaults to true. If disabled installation of images
+ will be quicker, but not as safe.
+
+`systemd-dissect`, `systemd-nspawn` and all other tools that may operate on
+disk images with `--image=` or similar:
+
+* `$SYSTEMD_DISSECT_VERITY_SIDECAR` — takes a boolean, which controls whether to
+ load "sidecar" Verity metadata files. If enabled (which is the default),
+ whenever a disk image is used, a set of files with the `.roothash`,
+ `.usrhash`, `.roothash.p7s`, `.usrhash.p7s`, `.verity` suffixes are searched
+ adjacent to disk image file, containing the Verity root hashes, their
+ signatures or the Verity data itself. If disabled this automatic discovery of
+ Verity metadata files is turned off.
+
+* `$SYSTEMD_DISSECT_VERITY_EMBEDDED` — takes a boolean, which controls whether
+ to load the embedded Verity signature data. If enabled (which is the
+ default), Verity root hash information and a suitable signature is
+ automatically acquired from a signature partition, following the
+ [Discoverable Partitions Specification](DISCOVERABLE_PARTITIONS.md).
+ If disabled any such partition is ignored. Note that this only disables
+ discovery of the root hash and its signature, the Verity data partition
+ itself is still searched in the GPT image.
+
+* `$SYSTEMD_DISSECT_VERITY_SIGNATURE` — takes a boolean, which controls whether
+ to validate the signature of the Verity root hash if available. If enabled
+ (which is the default), the signature of suitable disk images is validated
+ against any of the certificates in `/etc/verity.d/*.crt` (and similar
+ directories in `/usr/lib/`, `/run`, …) or passed to the kernel for validation
+ against its built-in certificates.
+
+* `$SYSTEMD_DISSECT_VERITY_TIMEOUT_SEC=sec` — takes a timespan, which controls
+ the timeout waiting for the image to be configured. Defaults to 100 msec.
+
+* `$SYSTEMD_LOOP_DIRECT_IO` – takes a boolean, which controls whether to enable
+ LO_FLAGS_DIRECT_IO (i.e. direct IO + asynchronous IO) on loopback block
+ devices when opening them. Defaults to on, set this to "0" to disable this
+ feature.
+
+`systemd-cryptsetup`:
+
+* `$SYSTEMD_CRYPTSETUP_USE_TOKEN_MODULE` – takes a boolean, which controls
+ whether to use the libcryptsetup "token" plugin module logic even when
+ activating via FIDO2, PKCS#11, TPM2, i.e. mechanisms natively supported by
+ `systemd-cryptsetup`. Defaults to enabled.
+
+Various tools that read passwords from the TTY, such as `systemd-cryptenroll`
+and `homectl`:
+
+* `$PASSWORD` — takes a string: the literal password to use. If this
+ environment variable is set it is used as password instead of prompting the
+ user interactively. This exists primarily for debugging and testing
+ purposes. Do not use this for production code paths, since environment
+ variables are typically inherited down the process tree without restrictions
+ and should thus not be used for secrets.
+
+* `$NEWPASSWORD` — similar to `$PASSWORD` above, but is used when both a
+ current and a future password are required, for example if the password is to
+ be changed. In that case `$PASSWORD` shall carry the current (i.e. old)
+ password and `$NEWPASSWORD` the new.
+
+`systemd-homed`:
+
+* `$SYSTEMD_HOME_ROOT` – defines an absolute path where to look for home
+ directories/images. When unspecified defaults to `/home/`. This is useful for
+ debugging purposes in order to run a secondary `systemd-homed` instance that
+ operates on a different directory where home directories/images are placed.
+
+* `$SYSTEMD_HOME_RECORD_DIR` – defines an absolute path where to look for
+ fixated home records kept on the host. When unspecified defaults to
+ `/var/lib/systemd/home/`. Similar to `$SYSTEMD_HOME_ROOT` this is useful for
+ debugging purposes, in order to run a secondary `systemd-homed` instance that
+ operates on a record database entirely separate from the host's.
+
+* `$SYSTEMD_HOME_DEBUG_SUFFIX` – takes a short string that is suffixed to
+ `systemd-homed`'s D-Bus and Varlink service names/sockets. This is also
+ understood by `homectl`. This too is useful for running an additional copy of
+ `systemd-homed` that doesn't interfere with the host's main one.
+
+* `$SYSTEMD_HOMEWORK_PATH` – configures the path to the `systemd-homework`
+ binary to invoke. If not specified defaults to
+ `/usr/lib/systemd/systemd-homework`.
+
+ Combining these four environment variables is pretty useful when
+ debugging/developing `systemd-homed`:
+```sh
+SYSTEMD_HOME_DEBUG_SUFFIX=foo \
+ SYSTEMD_HOMEWORK_PATH=/home/lennart/projects/systemd/build/systemd-homework \
+ SYSTEMD_HOME_ROOT=/home.foo/ \
+ SYSTEMD_HOME_RECORD_DIR=/var/lib/systemd/home.foo/ \
+ /home/lennart/projects/systemd/build/systemd-homed
+```
+
+* `$SYSTEMD_HOME_MOUNT_OPTIONS_BTRFS`, `$SYSTEMD_HOME_MOUNT_OPTIONS_EXT4`,
+ `$SYSTEMD_HOME_MOUNT_OPTIONS_XFS` – configure the default mount options to
+ use for LUKS home directories, overriding the built-in default mount
+ options. There's one variable for each of the supported file systems for the
+ LUKS home directory backend.
+
+`kernel-install`:
+
+* `$KERNEL_INSTALL_BYPASS` – If set to "1", execution of kernel-install is skipped
+ when kernel-install is invoked. This can be useful if kernel-install is invoked
+ unconditionally as a child process by another tool, such as package managers
+ running kernel-install in a postinstall script.
+
+`systemd-journald`:
+
+* `$SYSTEMD_JOURNAL_COMPACT` - Takes a boolean. If enabled, journal files are written
+ in a more compact format that reduces the amount of disk space required by the
+ journal. Note that journal files in compact mode are limited to 4G to allow use of
+ 32-bit offsets. Enabled by default.