Host System Administration

Proxmox Backup is based on the famous Debian Linux distribution. This means that you have access to the entire range of Debian packages, and that the base system is well documented. The Debian Administrator's Handbook is available online, and provides a comprehensive introduction to the Debian operating system.

A standard Proxmox Backup installation uses the default repositories from Debian, so you get bug fixes and security updates through that channel. In addition, we provide our own package repository to roll out all Proxmox related packages. This includes updates to some Debian packages when necessary.

We also deliver a specially optimized Linux kernel, based on the Ubuntu kernel. This kernel includes drivers for ZFS.

The following sections will concentrate on backup related topics. They will explain things which are different on Proxmox Backup, or tasks which are commonly used on Proxmox Backup. For other topics, please refer to the standard Debian documentation.

ZFS on Linux

ZFS is a combined file system and logical volume manager, designed by Sun Microsystems. There is no need to manually compile ZFS modules - all packages are included.

By using ZFS, it's possible to achieve maximum enterprise features with low budget hardware, and also high performance systems by leveraging SSD caching or even SSD only setups. ZFS can replace expensive hardware raid cards with moderate CPU and memory load, combined with easy management.

General advantages of ZFS:

  • Easy configuration and management with GUI and CLI.

  • Reliable

  • Protection against data corruption

  • Data compression on file system level

  • Snapshots

  • Copy-on-write clone

  • Various raid levels: RAID0, RAID1, RAID10, RAIDZ-1, RAIDZ-2 and RAIDZ-3

  • Can use SSD for cache

  • Self healing

  • Continuous integrity checking

  • Designed for high storage capacities

  • Asynchronous replication over network

  • Open Source

  • Encryption


ZFS depends heavily on memory, so it's recommended to have at least 8GB to start. In practice, use as much you can get for your hardware/budget. To prevent data corruption, we recommend the use of high quality ECC RAM.

If you use a dedicated cache and/or log disk, you should use an enterprise class SSD (for example, Intel SSD DC S3700 Series). This can increase the overall performance significantly.

IMPORTANT: Do not use ZFS on top of a hardware controller which has its own cache management. ZFS needs to directly communicate with disks. An HBA adapter or something like an LSI controller flashed in IT mode is recommended.

ZFS Administration

This section gives you some usage examples for common tasks. ZFS itself is really powerful and provides many options. The main commands to manage ZFS are zfs and zpool. Both commands come with extensive manual pages, which can be read with:

# man zpool
# man zfs

Create a new zpool

To create a new pool, at least one disk is needed. The ashift should have the same sector-size (2 power of ashift) or larger as the underlying disk.

# zpool create -f -o ashift=12 <pool> <device>

Create a new pool with RAID-0

Minimum 1 disk

# zpool create -f -o ashift=12 <pool> <device1> <device2>

Create a new pool with RAID-1

Minimum 2 disks

# zpool create -f -o ashift=12 <pool> mirror <device1> <device2>

Create a new pool with RAID-10

Minimum 4 disks

# zpool create -f -o ashift=12 <pool> mirror <device1> <device2> mirror <device3> <device4>

Create a new pool with RAIDZ-1

Minimum 3 disks

# zpool create -f -o ashift=12 <pool> raidz1 <device1> <device2> <device3>

Create a new pool with RAIDZ-2

Minimum 4 disks

# zpool create -f -o ashift=12 <pool> raidz2 <device1> <device2> <device3> <device4>

Create a new pool with cache (L2ARC)

It is possible to use a dedicated cache drive partition to increase the read performance (use SSDs).

For <device>, you can use multiple devices, as is shown in "Create a new pool with RAID*".

# zpool create -f -o ashift=12 <pool> <device> cache <cache_device>

Create a new pool with log (ZIL)

It is possible to use a dedicated cache drive partition to increase the write performance (use SSDs).

For <device>, you can use multiple devices, as is shown in "Create a new pool with RAID*".

# zpool create -f -o ashift=12 <pool> <device> log <log_device>

Add cache and log to an existing pool

You can add cache and log devices to a pool after its creation. In this example, we will use a single drive for both cache and log. First, you need to create 2 partitions on the SSD with parted or gdisk


Always use GPT partition tables.

The maximum size of a log device should be about half the size of physical memory, so this is usually quite small. The rest of the SSD can be used as cache.

# zpool add -f <pool> log <device-part1> cache <device-part2>

Changing a failed device

# zpool replace -f <pool> <old device> <new device>

Changing a failed bootable device

Depending on how Proxmox Backup was installed, it is either using grub or systemd-boot as a bootloader.

In either case, the first steps of copying the partition table, reissuing GUIDs and replacing the ZFS partition are the same. To make the system bootable from the new disk, different steps are needed which depend on the bootloader in use.

# sgdisk <healthy bootable device> -R <new device>
# sgdisk -G <new device>
# zpool replace -f <pool> <old zfs partition> <new zfs partition>


Use the zpool status -v command to monitor how far the resilvering process of the new disk has progressed.

With systemd-boot:

# proxmox-boot-tool format <new ESP>
# proxmox-boot-tool init <new ESP>


ESP stands for EFI System Partition, which is setup as partition #2 on bootable disks setup by the Proxmox Backup installer. For details, see Setting up a new partition for use as synced ESP.

With grub:

Usually grub.cfg is located in /boot/grub/grub.cfg

# grub-install <new disk>
# grub-mkconfig -o /path/to/grub.cfg

Activate e-mail notification

ZFS comes with an event daemon, ZED, which monitors events generated by the ZFS kernel module. The daemon can also send emails upon ZFS events, such as pool errors. Newer ZFS packages ship the daemon in a separate package zfs-zed, which should already be installed by default in Proxmox Backup.

You can configure the daemon via the file /etc/zfs/zed.d/zed.rc, using your preferred editor. The required setting for email notification is ZED_EMAIL_ADDR, which is set to root by default.


Please note that Proxmox Backup forwards mails to root to the email address configured for the root user.

Limit ZFS memory usage

It is good to use at most 50 percent (which is the default) of the system memory for ZFS ARC, to prevent performance degradation of the host. Use your preferred editor to change the configuration in /etc/modprobe.d/zfs.conf and insert:

options zfs zfs_arc_max=8589934592

The above example limits the usage to 8 GiB ('8 * 2^30^').


In case your desired zfs_arc_max value is lower than or equal to zfs_arc_min (which defaults to 1/32 of the system memory), zfs_arc_max will be ignored. Thus, for it to work in this case, you must set zfs_arc_min to at most zfs_arc_max - 1. This would require updating the configuration in /etc/modprobe.d/zfs.conf, with:

options zfs zfs_arc_min=8589934591
options zfs zfs_arc_max=8589934592

This example setting limits the usage to 8 GiB ('8 * 2^30^') on systems with more than 256 GiB of total memory, where simply setting zfs_arc_max alone would not work.


If your root file system is ZFS, you must update your initramfs every time this value changes.

# update-initramfs -u

Swap on ZFS

Swap-space created on a zvol may cause some issues, such as blocking the server or generating a high IO load.

We strongly recommend using enough memory, so that you normally do not run into low memory situations. Should you need or want to add swap, it is preferred to create a partition on a physical disk and use it as a swap device. You can leave some space free for this purpose in the advanced options of the installer. Additionally, you can lower the swappiness value. A good value for servers is 10:

# sysctl -w vm.swappiness=10

To make the swappiness persistent, open /etc/sysctl.conf with an editor of your choice and add the following line:

vm.swappiness = 10
Linux kernel swappiness parameter values



vm.swappiness = 0

The kernel will swap only to avoid an 'out of memory' condition

vm.swappiness = 1

Minimum amount of swapping without disabling it entirely.

vm.swappiness = 10

Sometimes recommended to improve performance when sufficient memory exists in a system.

vm.swappiness = 60

The default value.

vm.swappiness = 100

The kernel will swap aggressively.

ZFS compression

To activate compression:

# zpool set compression=lz4 <pool>

We recommend using the lz4 algorithm, since it adds very little CPU overhead. Other algorithms such as lzjb, zstd and gzip-N (where N is an integer from 1-9 representing the compression ratio, where 1 is fastest and 9 is best compression) are also available. Depending on the algorithm and how compressible the data is, having compression enabled can even increase I/O performance.

You can disable compression at any time with:

# zfs set compression=off <dataset>

Only new blocks will be affected by this change.

ZFS special device

Since version 0.8.0, ZFS supports special devices. A special device in a pool is used to store metadata, deduplication tables, and optionally small file blocks.

A special device can improve the speed of a pool consisting of slow spinning hard disks with a lot of metadata changes. For example, workloads that involve creating, updating or deleting a large number of files will benefit from the presence of a special device. ZFS datasets can also be configured to store small files on the special device, which can further improve the performance. Use fast SSDs for the special device.


The redundancy of the special device should match the one of the pool, since the special device is a point of failure for the entire pool.


Adding a special device to a pool cannot be undone!

To create a pool with special device and RAID-1:

# zpool create -f -o ashift=12 <pool> mirror <device1> <device2> special mirror <device3> <device4>

Adding a special device to an existing pool with RAID-1:

# zpool add <pool> special mirror <device1> <device2>

ZFS datasets expose the special_small_blocks=<size> property. size can be 0 to disable storing small file blocks on the special device, or a power of two in the range between 512B to 128K. After setting this property, new file blocks smaller than size will be allocated on the special device.


If the value for special_small_blocks is greater than or equal to the recordsize (default 128K) of the dataset, all data will be written to the special device, so be careful!

Setting the special_small_blocks property on a pool will change the default value of that property for all child ZFS datasets (for example, all containers in the pool will opt in for small file blocks).

Opt in for all files smaller than 4K-blocks pool-wide:

# zfs set special_small_blocks=4K <pool>

Opt in for small file blocks for a single dataset:

# zfs set special_small_blocks=4K <pool>/<filesystem>

Opt out from small file blocks for a single dataset:

# zfs set special_small_blocks=0 <pool>/<filesystem>


Corrupt cache file

zfs-import-cache.service imports ZFS pools using the ZFS cache file. If this file becomes corrupted, the service won't be able to import the pools that it's unable to read from it.

As a result, in case of a corrupted ZFS cache file, some volumes may not be mounted during boot and must be mounted manually later.

For each pool, run:

# zpool set cachefile=/etc/zfs/zpool.cache POOLNAME

then, update the initramfs by running:

# update-initramfs -u -k all

and finally, reboot the node.

Another workaround to this problem is enabling the zfs-import-scan.service, which searches and imports pools via device scanning (usually slower).

Host Bootloader

Proxmox Backup currently uses one of two bootloaders, depending on the disk setup selected in the installer.

For EFI Systems installed with ZFS as the root filesystem systemd-boot is used, unless Secure Boot is enabled. All other deployments use the standard grub bootloader (this usually also applies to systems which are installed on top of Debian).

Partitioning Scheme Used by the Installer

The Proxmox Backup installer creates 3 partitions on all disks selected for installation.

The created partitions are:

  • A 1 MB BIOS Boot Partition (gdisk type EF02)

  • A 512 MB EFI System Partition (ESP, gdisk type EF00)

  • A third partition spanning the configured hdsize parameter or the remaining space available for the chosen storage type

Systems using ZFS as a root filesystem are booted with a kernel and initrd image stored on the 512 MB EFI System Partition. For legacy BIOS systems, and EFI systems with Secure Boot enabled, grub is used, for EFI systems without Secure Boot, systemd-boot is used. Both are installed and configured to point to the ESPs.

grub in BIOS mode (--target i386-pc) is installed onto the BIOS Boot Partition of all selected disks on all systems booted with grub (that is, all installs with root on ext4 or xfs, and installs with root on ZFS on non-EFI systems).

Synchronizing the Content of the ESP with proxmox-boot-tool

proxmox-boot-tool is a utility used to keep the contents of the EFI System Partitions properly configured and synchronized. It copies certain kernel versions to all ESPs and configures the respective bootloader to boot from the vfat formatted ESPs. In the context of ZFS as root filesystem, this means that you can use all the optional features on your root pool, instead of the subset which is also present in the ZFS implementation in grub or having to create a small, separate boot-pool (see: Booting ZFS on root with grub).

In setups with redundancy, all disks are partitioned with an ESP by the installer. This ensures the system boots, even if the first boot device fails or if the BIOS can only boot from a particular disk.

The ESPs are not kept mounted during regular operation. This helps to prevent filesystem corruption in the vfat formatted ESPs in case of a system crash, and removes the need to manually adapt /etc/fstab in case the primary boot device fails.

proxmox-boot-tool handles the following tasks:

  • Formatting and setting up a new partition

  • Copying and configuring new kernel images and initrd images to all listed ESPs

  • Synchronizing the configuration on kernel upgrades and other maintenance tasks

  • Managing the list of kernel versions which are synchronized

  • Configuring the boot-loader to boot a particular kernel version (pinning)

You can view the currently configured ESPs and their state by running:

# proxmox-boot-tool status

Setting up a New Partition for use as Synced ESP

To format and initialize a partition as synced ESP, for example, after replacing a failed vdev in an rpool, proxmox-boot-tool from proxmox-kernel-helper can be used.


the format command will format the <partition>. Make sure to pass in the right device/partition!

For example, to format an empty partition /dev/sda2 as ESP, run the following:

# proxmox-boot-tool format /dev/sda2

To setup an existing, unmounted ESP located on /dev/sda2 for inclusion in Proxmox Backup's kernel update synchronization mechanism, use the following:

# proxmox-boot-tool init /dev/sda2


# proxmox-boot-tool init /dev/sda2 grub

to force initialization with Grub instead of systemd-boot, for example for Secure Boot support.

Following this, /etc/kernel/proxmox-boot-uuids` should contain a new line with the UUID of the newly added partition. The init command will also automatically trigger a refresh of all configured ESPs.

Updating the Configuration on all ESPs

To copy and configure all bootable kernels and keep all ESPs listed in /etc/kernel/proxmox-boot-uuids in sync, you just need to run:

# proxmox-boot-tool refresh

(Equivalent to running update-grub on systems with ext4 or xfs on root).

This is necessary after making changes to the kernel commandline, or if you want to sync all kernels and initrds.


Both update-initramfs and apt (when necessary) will automatically trigger a refresh.

Kernel Versions Considered by proxmox-boot-tool

The following kernel versions are configured by default:

  • The currently running kernel

  • The version being newly installed on package updates

  • The two latest, already installed kernels

  • The latest version of the second-to-last kernel series (e.g. 5.0, 5.3), if applicable

  • Any manually selected kernels

Manually Keeping a Kernel Bootable

Should you wish to add a certain kernel and initrd image to the list of bootable kernels, use proxmox-boot-tool kernel add.

For example, run the following to add the kernel with ABI version 5.0.15-1-pve to the list of kernels to keep installed and synced to all ESPs:

# proxmox-boot-tool kernel add 5.0.15-1-pve

proxmox-boot-tool kernel list will list all kernel versions currently selected for booting:

# proxmox-boot-tool kernel list
Manually selected kernels:

Automatically selected kernels:

Run proxmox-boot-tool kernel remove to remove a kernel from the list of manually selected kernels, for example:

# proxmox-boot-tool kernel remove 5.0.15-1-pve


It's required to run proxmox-boot-tool refresh to update all EFI System Partitions (ESPs) after a manual kernel addition or removal from above.

Determine which Bootloader is Used

Grub boot screen

The simplest and most reliable way to determine which bootloader is used, is to watch the boot process of the Proxmox Backup node.

You will either see the blue box of grub or the simple black on white systemd-boot.

systemd-boot screen

Determining the bootloader from a running system might not be 100% accurate. The most reliable way is to run the following command:

# efibootmgr -v

If it returns a message that EFI variables are not supported, grub is used in BIOS/Legacy mode.

If the output contains a line that looks similar to the following, grub is used in UEFI mode.

Boot0005* proxmox     [...] File(\EFI\proxmox\grubx64.efi)

If the output contains a line similar to the following, systemd-boot is used.

Boot0006* Linux Boot Manager  [...] File(\EFI\systemd\systemd-bootx64.efi)

By running the following command, you can find out if proxmox-boot-tool is configured, which is a good indication of how the system is booted:

# proxmox-boot-tool status


grub has been the de facto standard for booting Linux systems for many years and is quite well documented (see the Grub Manual).


Changes to the grub configuration are done via the defaults file /etc/default/grub or via config snippets in /etc/default/grub.d. To regenerate the configuration file after a change to the configuration, run:

# update-grub


Systems using proxmox-boot-tool will call proxmox-boot-tool refresh upon update-grub


systemd-boot is a lightweight EFI bootloader. It reads the kernel and initrd images directly from the EFI Service Partition (ESP) where it is installed. The main advantage of directly loading the kernel from the ESP is that it does not need to reimplement the drivers for accessing the storage. In Proxmox Backup, proxmox-boot-tool is used to keep the configuration on the ESPs synchronized.


systemd-boot is configured via the file loader/loader.conf in the root directory of an EFI System Partition (ESP). See the loader.conf(5) manpage for details.

Each bootloader entry is placed in a file of its own, in the directory loader/entries/

An example entry.conf looks like this (/ refers to the root of the ESP):

title    Proxmox
version  5.0.15-1-pve
options   root=ZFS=rpool/ROOT/pve-1 boot=zfs
linux    /EFI/proxmox/5.0.15-1-pve/vmlinuz-5.0.15-1-pve
initrd   /EFI/proxmox/5.0.15-1-pve/initrd.img-5.0.15-1-pve

Editing the Kernel Commandline

You can modify the kernel commandline in the following places, depending on the bootloader used:


The kernel commandline needs to be placed in the variable GRUB_CMDLINE_LINUX_DEFAULT in the file /etc/default/grub. Running update-grub appends its content to all linux entries in /boot/grub/grub.cfg.


The kernel commandline needs to be placed as one line in /etc/kernel/cmdline. To apply your changes, run proxmox-boot-tool refresh, which sets it as the option line for all config files in loader/entries/proxmox-*.conf.

Override the Kernel-Version for next Boot

To select a kernel that is not currently the default kernel, you can either:

  • Use the boot loader menu that is displayed at the beginning of the boot process

  • Use the proxmox-boot-tool to pin the system to a kernel version either once or permanently (until pin is reset).

This should help you work around incompatibilities between a newer kernel version and the hardware.


Such a pin should be removed as soon as possible, so that all recent security patches from the latest kernel are also applied to the system.

For example, to permanently select the version 5.15.30-1-pve for booting, you would run:

# proxmox-boot-tool kernel pin 5.15.30-1-pve


The pinning functionality works for all Proxmox Backup systems, not only those using proxmox-boot-tool to synchronize the contents of the ESPs, if your system does not use proxmox-boot-tool for synchronizing, you can also skip the proxmox-boot-tool refresh call in the end.

You can also set a kernel version to be booted on the next system boot only. This is useful, for example, to test if an updated kernel has resolved an issue, which caused you to pin a version in the first place:

# proxmox-boot-tool kernel pin 5.15.30-1-pve --next-boot

To remove any pinned version configuration, use the unpin subcommand:

# proxmox-boot-tool kernel unpin

While unpin has a --next-boot option as well, it is used to clear a pinned version set with --next-boot. As that happens already automatically on boot, invoking it manually is of little use.

After setting or clearing pinned versions, you also need to synchronize the content and configuration on the ESPs by running the refresh subcommand.


You will be prompted to automatically do for proxmox-boot-tool managed systems if you call the tool interactively.

# proxmox-boot-tool refresh

Secure Boot

Since Proxmox Backup 3.1, Secure Boot is supported out of the box via signed packages and integration in proxmox-boot-tool.

The following packages need to be installed for Secure Boot to be enabled:

  • shim-signed (shim bootloader signed by Microsoft)

  • shim-helpers-amd64-signed (fallback bootloader and MOKManager, signed by Proxmox)

  • grub-efi-amd64-signed (Grub EFI bootloader, signed by Proxmox)

  • proxmox-kernel-6.X.Y-Z-pve-signed (Kernel image, signed by Proxmox)

Only Grub as bootloader is supported out of the box, since there are no other pre-signed bootloader packages available. Any new installation of Proxmox Backup will automatically have all of the above packages included.

More details about how Secure Boot works, and how to customize the setup, are available in our wiki.

Switching an Existing Installation to Secure Boot


This can lead to an unbootable installation in some cases if not done correctly. Reinstalling the host will setup Secure Boot automatically if available, without any extra interactions. Make sure you have a working and well-tested backup of your Proxmox Backup host!

An existing UEFI installation can be switched over to Secure Boot if desired, without having to reinstall Proxmox Backup from scratch.

First, ensure all your system is up-to-date. Next, install all the required pre-signed packages as listed above. Grub automatically creates the needed EFI boot entry for booting via the default shim.


If systemd-boot is used as a bootloader (see Determine which Bootloader is used), some additional setup is needed. This is only the case if Proxmox Backup was installed with ZFS-on-root.

To check the latter, run:

# findmnt /

If the host is indeed using ZFS as root filesystem, the FSTYPE column should contain zfs:

/      rpool/ROOT/pbs-1 zfs    rw,relatime,xattr,noacl

Next, a suitable potential ESP (EFI system partition) must be found. This can be done using the lsblk command as following:

# lsblk -o +FSTYPE

The output should look something like this:

sda      8:0    0   32G  0 disk
├─sda1   8:1    0 1007K  0 part
├─sda2   8:2    0  512M  0 part             vfat
└─sda3   8:3    0 31.5G  0 part             zfs_member
sdb      8:16   0   32G  0 disk
├─sdb1   8:17   0 1007K  0 part
├─sdb2   8:18   0  512M  0 part             vfat
└─sdb3   8:19   0 31.5G  0 part             zfs_member

In this case, the partitions sda2 and sdb2 are the targets. They can be identified by the their size of 512M and their FSTYPE being vfat, in this case on a ZFS RAID-1 installation.

These partitions must be properly set up for booting through Grub using proxmox-boot-tool. This command (using sda2 as an example) must be run separately for each individual ESP:

# proxmox-boot-tool init /dev/sda2 grub

Afterwards, you can sanity-check the setup by running the following command:

# efibootmgr -v

This list should contain an entry looking similar to this:

Boot0009* proxmox       HD(2,GPT,..,0x800,0x100000)/File(\EFI\proxmox\shimx64.efi)


The old systemd-boot bootloader will be kept, but Grub will be preferred. This way, if booting using Grub in Secure Boot mode does not work for any reason, the system can still be booted using systemd-boot with Secure Boot turned off.

Now the host can be rebooted and Secure Boot enabled in the UEFI firmware setup utility.

On reboot, a new entry named proxmox should be selectable in the UEFI firmware boot menu, which boots using the pre-signed EFI shim.

If, for any reason, no proxmox entry can be found in the UEFI boot menu, you can try adding it manually (if supported by the firmware), by adding the file \EFI\proxmox\shimx64.efi as a custom boot entry.


Some UEFI firmwares are known to drop the proxmox boot option on reboot. This can happen if the proxmox boot entry is pointing to a Grub installation on a disk, where the disk itself is not a boot option. If possible, try adding the disk as a boot option in the UEFI firmware setup utility and run proxmox-boot-tool again.


To enroll custom keys, see the accompanying Secure Boot wiki page.

Using DKMS/Third Party Modules With Secure Boot

On systems with Secure Boot enabled, the kernel will refuse to load modules which are not signed by a trusted key. The default set of modules shipped with the kernel packages is signed with an ephemeral key embedded in the kernel image which is trusted by that specific version of the kernel image.

In order to load other modules, such as those built with DKMS or manually, they need to be signed with a key trusted by the Secure Boot stack. The easiest way to achieve this is to enroll them as Machine Owner Key (MOK) with mokutil.

The dkms tool will automatically generate a keypair and certificate in /var/lib/dkms/mok.key and /var/lib/dkms/ and use it for signing the kernel modules it builds and installs.

You can view the certificate contents with

# openssl x509 -in /var/lib/dkms/ -noout -text

and enroll it on your system using the following command:

# mokutil --import /var/lib/dkms/
input password:
input password again:

The mokutil command will ask for a (temporary) password twice, this password needs to be entered one more time in the next step of the process! Rebooting the system should automatically boot into the MOKManager EFI binary, which allows you to verify the key/certificate and confirm the enrollment using the password selected when starting the enrollment using mokutil. Afterwards, the kernel should allow loading modules built with DKMS (which are signed with the enrolled MOK). The MOK can also be used to sign custom EFI binaries and kernel images if desired.

The same procedure can also be used for custom/third-party modules not managed with DKMS, but the key/certificate generation and signing steps need to be done manually in that case.

Certificate Management

Access to the API and thus the web-based administration interface is always encrypted through https. Each Proxmox Backup host creates by default its own (self-signed) certificate. This certificate is used for encrypted communication with the host’s proxmox-backup-proxy service, for any API call between a user or backup-client and the web-interface.

Certificate verification when sending backups to a Proxmox Backup Server is either done based on pinning the certificate fingerprints in the storage/remote configuration, or by using certificates, signed by a trusted certificate authority.

Certificates for the API and SMTP

Proxmox Backup stores its certificate and key in:

  • /etc/proxmox-backup/proxy.pem

  • /etc/proxmox-backup/proxy.key

You have the following options for the certificate:

  1. Keep using the default self-signed certificate in /etc/proxmox-backup/proxy.pem.

  2. Use an externally provided certificate (for example, signed by a commercial Certificate Authority (CA)).

  3. Use an ACME provider like Let’s Encrypt to get a trusted certificate with automatic renewal; this is also integrated in the Proxmox Backup API and web interface.

Certificates are managed through the Proxmox Backup web-interface/API or using the proxmox-backup-manager CLI tool.

Upload Custom Certificate

If you already have a certificate which you want to use for a Proxmox Mail Gateway host, you can simply upload that certificate over the web interface.

Upload a custom certificate

Note that any certificate key files must not be password protected.

Trusted certificates via Let’s Encrypt (ACME)

Proxmox Backup includes an implementation of the Automatic Certificate Management Environment (ACME) protocol, allowing Proxmox Backup admins to use an ACME provider like Let’s Encrypt for easy setup of TLS certificates, which are accepted and trusted by modern operating systems and web browsers out of the box.

Currently, the two ACME endpoints implemented are the Let’s Encrypt (LE) production and staging environments. Our ACME client supports validation of http-01 challenges using a built-in web server and validation of dns-01 challenges using a DNS plugin supporting all the DNS API endpoints does.

ACME Account

Create ACME Account

You need to register an ACME account per cluster, with the endpoint you want to use. The email address used for that account will serve as the contact point for renewal-due or similar notifications from the ACME endpoint.

You can register or deactivate ACME accounts over the web interface Certificates -> ACME Accounts or using the proxmox-backup-manager command-line tool.

proxmox-backup-manager acme account register <account-name> <>


Because of rate-limits you should use LE staging for experiments or if you use ACME for the very first time until all is working there, and only then switch over to the production directory.

ACME Plugins

The ACME plugin’s role is to provide automatic verification that you, and thus the Proxmox Backup Server under your operation, are the real owner of a domain. This is the basic building block of automatic certificate management.

The ACME protocol specifies different types of challenges, for example the http-01, where a web server provides a file with a specific token to prove that it controls a domain. Sometimes this isn’t possible, either because of technical limitations or if the address of a record is not reachable from the public internet. The dns-01 challenge can be used in such cases. This challenge is fulfilled by creating a certain DNS record in the domain’s zone.

Create ACME Account

Proxmox Backup supports both of those challenge types out of the box, you can configure plugins either over the web interface under Certificates -> ACME Challenges, or using the proxmox-backup-manager acme plugin add command.

ACME Plugin configurations are stored in /etc/proxmox-backup/acme/plugins.cfg.


You can add new or manage existing domain entries under Certificates, or using the proxmox-backup-manager command.

Add a Domain for ACME verification

After configuring the desired domain(s) for a node and ensuring that the desired ACME account is selected, you can order your new certificate over the web-interface. On success, the interface will reload after roughly 10 seconds.

Renewal will happen automatically

ACME HTTP Challenge Plugin

There is always an implicitly configured standalone plugin for validating http-01 challenges via the built-in web server spawned on port 80.


The name standalone means that it can provide the validation on its own, without any third party service.

There are a few prerequisites to use this for certificate management with Let’s Encrypts ACME.

  • You have to accept the ToS of Let’s Encrypt to register an account.

  • Port 80 of the node needs to be reachable from the internet.

  • There must be no other listener on port 80.

  • The requested (sub)domain needs to resolve to a public IP of the Proxmox Backup host.

ACME DNS API Challenge Plugin

On systems where external access for validation via the http-01 method is not possible or desired, it is possible to use the dns-01 validation method. This validation method requires a DNS server that allows provisioning of TXT records via an API.

Configuring ACME DNS APIs for validation

Proxmox Backup re-uses the DNS plugins developed for the [1] project. Please refer to its documentation for details on configuration of specific APIs.

The easiest way to configure a new plugin with the DNS API is using the web interface (Certificates -> ACME Accounts/Challenges).

Here you can add a new challenge plugin by selecting your API provider and entering the credential data to access your account over their API.


See the How to use DNS API wiki for more detailed information about getting API credentials for your provider. Configuration values do not need to be quoted with single or double quotes; for some plugins that is even an error.

As there are many DNS providers and API endpoints, Proxmox Backup automatically generates the form for the credentials, but not all providers are annotated yet. For those you will see a bigger text area, into which you simply need to copy all the credential’s KEY=VALUE pairs.

DNS Validation through CNAME Alias

A special alias mode can be used to handle validation on a different domain/DNS server, in case your primary/real DNS does not support provisioning via an API. Manually set up a permanent CNAME record for _acme-challenge.domain1.example pointing to _acme-challenge.domain2.example, and set the alias property in the Proxmox Backup node configuration file /etc/proxmox-backup/node.cfg to domain2.example to allow the DNS server of domain2.example to validate all challenges for domain1.example.

Wildcard Certificates

Wildcard DNS names start with a *. prefix and are considered valid for all (one-level) subdomain names of the verified domain. So a certificate for *.domain.example is valid for foo.domain.example and bar.domain.example, but not for

Currently, you can only create wildcard certificates with the DNS challenge type.

Combination of Plugins

Combining http-01 and dns-01 validation is possible in case your node is reachable via multiple domains with different requirements / DNS provisioning capabilities. Mixing DNS APIs from multiple providers or instances is also possible by specifying different plugin instances per domain.


Accessing the same service over multiple domains increases complexity and should be avoided if possible.

Automatic renewal of ACME certificates

If a node has been successfully configured with an ACME-provided certificate (either via proxmox-backup-manager or via the web-interface/API), the certificate will be renewed automatically by the proxmox-backup-daily-update.service. Currently, renewal is triggered if the certificate either has already expired or if it will expire in the next 30 days.

Manually Change Certificate over the Command Line

If you want to get rid of certificate verification warnings, you have to generate a valid certificate for your server.

Log in to your Proxmox Backup via ssh or use the console:

openssl req -newkey rsa:2048 -nodes -keyout key.pem -out req.pem

Follow the instructions on the screen, for example:

Country Name (2 letter code) [AU]: AT
State or Province Name (full name) [Some-State]:Vienna
Locality Name (eg, city) []:Vienna
Organization Name (eg, company) [Internet Widgits Pty Ltd]: Proxmox GmbH
Organizational Unit Name (eg, section) []:Proxmox Backup
Common Name (eg, YOUR name) []:
Email Address []

Please enter the following 'extra' attributes to be sent with your certificate request
A challenge password []: not necessary
An optional company name []: not necessary

After you have finished the certificate request, you have to send the file req.pem to your Certification Authority (CA). The CA will issue the certificate (BASE64 encoded), based on your request – save this file as cert.pem to your Proxmox Backup.

To activate the new certificate, do the following on your Proxmox Backup

cp key.pem /etc/proxmox-backup/proxy.key
cp cert.pem /etc/proxmox-backup/proxy.pem

Then restart the API servers:

systemctl restart proxmox-backup-proxy

Test your new certificate, using your browser.


To transfer files to and from your Proxmox Backup, you can use secure copy: If your desktop runs Linux, you can use the scp command-line tool. If your desktop PC runs windows, please use an scp client like WinSCP (see

Service Daemons


This daemon exposes the whole Proxmox Backup Server API on TCP port 8007 using HTTPS. It runs as user backup and has very limited permissions. Operations requiring more permissions are forwarded to the local proxmox-backup service.


This daemon exposes the Proxmox Backup Server management API on It runs as root and has permission to do all privileged operations.

NOTE: The daemon listens to a local address only, so you cannot access it from outside. The proxmox-backup-proxy daemon exposes the API to the outside world.

Command-line Tools


This tool implements a backup server client, i.e. it can connect to a backup servers to issue management commands and to create or restore backups.


This tool exposes the whole backup server management API on the command line.


This tool can configure and manage tape backups.


The pmt command controls Linux tape devices.


The pmtx command controls SCSI media changer devices (tape autoloader).


pxar is a command-line utility for creating and manipulating archives in the Proxmox File Archive Format (.pxar). It is inspired by casync file archive format, which caters to a similar use-case. The .pxar format is adapted to fulfill the specific needs of the Proxmox Backup Server, for example, efficient storage of hard links. The format is designed to reduce the required storage on the server by achieving a high level of deduplication.

Creating an Archive

Run the following command to create an archive of a folder named source:

# pxar create archive.pxar /path/to/source

This will create a new archive called archive.pxar with the contents of the source folder.


pxar will not overwrite any existing archives. If an archive with the same name is already present in the target folder, the creation will fail.

By default, pxar will skip certain mount points and will not follow device boundaries. This design decision is based on the primary use case of creating archives for backups. It makes sense to ignore the contents of certain temporary or system specific files in a backup. To alter this behavior and follow device boundaries, use the --all-file-systems flag.

It is possible to exclude certain files and/or folders from the archive by passing the --exclude parameter with gitignore-style match patterns.

For example, you can exclude all files ending in .txt from the archive by running:

# pxar create archive.pxar /path/to/source --exclude '**/*.txt'

Be aware that the shell itself will try to expand glob patterns before invoking pxar. In order to avoid this, all globs have to be quoted correctly.

It is possible to pass the --exclude parameter multiple times, in order to match more than one pattern. This allows you to use more complex file inclusion/exclusion behavior. However, it is recommended to use .pxarexclude files instead for such cases.

For example you might want to exclude all .txt files except a specific one from the archive. This would be achieved via the negated match pattern, prefixed by !. All the glob patterns are relative to the source directory.

# pxar create archive.pxar /path/to/source --exclude '**/*.txt' --exclude '!/folder/file.txt'


The order of the glob match patterns matters, as later ones override earlier ones. Permutations of the same patterns lead to different results.

pxar will store the list of glob match patterns passed as parameters via the command line, in a file called .pxarexclude-cli, at the root of the archive. If a file with this name is already present in the source folder during archive creation, this file is not included in the archive, and the file containing the new patterns is added to the archive instead. The original file is not altered.

A more convenient and persistent way to exclude files from the archive is by placing the glob match patterns in .pxarexclude files. It is possible to create and place these files in any directory of the filesystem tree. These files must contain one pattern per line, and later patterns override earlier ones. The patterns control file exclusions of files present within the given directory or further below it in the tree. The behavior is the same as described in Creating Backups.

Extracting an Archive

An existing archive, archive.pxar, is extracted to a target directory with the following command:

# pxar extract archive.pxar /path/to/target

If no target is provided, the contents of the archive is extracted to the current working directory.

In order to restore only parts of an archive, single files, and/or folders, it is possible to pass the corresponding glob match patterns as additional parameters or to use the patterns stored in a file:

# pxar extract etc.pxar /restore/target/etc --pattern '**/*.conf'

The above example restores all .conf files encountered in any of the sub-folders in the archive etc.pxar to the target /restore/target/etc. A path to the file containing match patterns can be specified using the --files-from parameter.

List the Contents of an Archive

To display the files and directories contained in an archive archive.pxar, run the following command:

# pxar list archive.pxar

This displays the full path of each file or directory with respect to the archive's root.

Mounting an Archive

pxar allows you to mount and inspect the contents of an archive via FUSE. In order to mount an archive named archive.pxar to the mount point /mnt, run the command:

# pxar mount archive.pxar /mnt

Once the archive is mounted, you can access its content under the given mount point.

# cd /mnt
# ls
bin   dev  home  lib32  libx32      media  opt   root  sbin  sys  usr
boot  etc  lib   lib64  lost+found  mnt    proc  run   srv   tmp  var


Command-line tool for restoring files and directories from Proxmox Backup archives. In contrast to proxmox-backup-client, this supports both container/host and VM backups.


Implements debugging functionality to inspect Proxmox Backup datastore files, verify the integrity of chunks.

The 'diff' subcommand allows comparing .pxar archives for two arbitrary snapshots. A list of added/modified/deleted files will be displayed.

Also contains an 'api' subcommand where arbitrary api paths can be called (get/create/set/delete) as well as display their parameters (usage) and their child-links (ls).

By default, it connects to the proxmox-backup-proxy on localhost via https, but by setting the environment variable PROXMOX_DEBUG_API_CODE to 1 the tool directly calls the corresponding code.


Using PROXMOX_DEBUG_API_CODE can be dangerous and is only intended for debugging purposes. It is not intended for use on a production system.