Proxmox has a pretty good backup scheduler, but it relies on the backup destination being mounted as a storage location. This implies that the backup destination needs to be a protocol that Proxmox supports - SMB (CIFS), NFS, … or Proxmox Backup Server. If you want to push your backups to a cloud service, you probably need something a bit more complicated. Thankfully, Proxmox’s backup scheduler thought about this and has a hook feature we can use for this purpose, and we can use any protocol supported on the Debian base system, including things such as FUSE or s3cmd.

In this project, I integrate S3 object storage with the Proxmox backup scheduler, copying resulting backups to a cloud storage service directly from the Proxmox system. The S3 protocol is ubiquitous among cloud object storage providers, so we aren’t tied to AWS - we can use any service such as Backblaze. In my case, I’m demonstrating this with Linode.



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Proxmox VZDump hook scripting

Proxmox’s documentation mentions briefly that the --script argument can be passed to vzdump, the Proxmox backup utility. We can also add the line script <path_to_script> in the /etc/pve/jobs.conf file, and it will retain this script argument even if you modify the backup job from the GUI. You can’t add a script command from the GUI, but you need to initially create the job there.

Proxmox mentions a backup file (, but I was unable to find a copy easily. For your convenience, I’ve uploaded it to my site here for you to view. The tl;dr is that:

  • The first argument to the script is the phase, which is one of:
    • job-start
    • job-end
    • job-abort
    • backup-start
    • backup-end
    • backup-abort
    • log-end
    • pre-stop
    • pre-restart
    • post-restart
  • The ‘job’ type phases are called once for a job, while the rest are called for each backup in the job
  • The backup mode (stop/suspend/snapshot) and vmid are passed as arguments to the non-job types
  • Additional information is passed as environment variables for certain phases, including TARGET (the full path on the local system to the backup file), LOGFILE (the full path to the log file), and a few other useful attributes.

In our case, we are going to hook to the job-end, backup-end, and log-end phases and do the following:

  • For backup-end, copy the file TARGET to the S3 bucket and delete the original
  • For log-end, copy the file LOGFILE to the S3 bucket and delete the original
  • For job-end, check if there are any backups which should be expired and remove them. This is done only once, even if there are multiple VMs to backup in a single job.

S3 Tools

There are a few different open source options for general purpose file management using the S3 protocol. The most common are s3cmd and s3fs-fuse. The first provides a command line utility to perform actions on an S3 bucket (ls, put, get, delete, …) and the second implements a filesystem backed by an S3 bucket. Since the S3 protocol can only replace files (not modify parts of a file), s3fs-fuse can be quite slow depending on how files are written/read. Given the use of hook scripts here, I’ve decided to use s3cmd. It’s easily installed by running apt install s3cmd on Proxmox.

Once s3cmd is installed, we need to configure it by running s3cmd --configure. It will ask you a few questions, and the answers will depend on your cloud storage provider. They should have a guide on configuring S3 access with their service (i.e. Linode’s is here). I’ve walked through my own setup in the video.

Once we run configure, it will generate a file called ~/.s3cfg which includes the access key and endpoint URL. Since we ran this as root, it will be /root/.s3cfg on our Proxmox host. That’s fine, since backup jobs run as root.

If you’re interested in the details, feel free to read the s3cmd docs here.

Once you’ve verified that you have s3cmd installed and can s3cmd ls and s3cmd put to the target bucket, we can add the s3 put’s to our backup script.

Backup Expiration Script

I found a script to handle expiration of files in S3. I’ve copied it here for reference. I named it on my system.


# Usage: ./ "bucketname" "7 days"

s3cmd ls s3://$1 | grep " DIR " -v | while read -r line;
    createDate=`echo $line|awk {'print $1" "$2'}`
    createDate=$(date -d "$createDate" "+%s")
    olderThan=$(date -d "$2 ago" "+%s")
    if [[ $createDate -le $olderThan ]];
        fileName=`echo $line|awk {'print $4'}`
        if [ $fileName != "" ]
            printf 'Deleting "%s"\n' $fileName
            s3cmd del "$fileName"

Don’t forget to chmod +x it once you are done.

Final Backup Script

Here is the final backup script which you can copy to your system. Again, don’t forget to chmod +x it.

#!/usr/bin/perl -w
# Hook script for vzdump to backup to an S3 bucket
# 2022 Andrew Palardy
# Based on example hook script from Proxmox

use strict;

# Define the name of your bucket here
my $bucket = "apalrd-proxmox";
# The S3 endpoint comes from the s3cmd --configure setup, it is not set here

# Define the number of days to retain backups in the bucket
# Only accepts days, doesn't check hours/minutes
my $retain = 30;

#Uncomment this to see the hook script with arguments (not required)
#print "HOOK: " . join (' ', @ARGV) . "\n";

#Get the phase from the first argument
my $phase = shift;

#For job-based phases
#Note that job-init was added in PVE 7.2 or 7.3 AFAIK
if (    $phase eq 'job-init'  ||
        $phase eq 'job-start' || 
        $phase eq 'job-end'   || 
        $phase eq 'job-abort') { 

        #Env variables available for job based arguments
        my $dumpdir = $ENV{DUMPDIR};

        my $storeid = $ENV{STOREID};

        #Uncomment this to print the environment variables for debugging
        #print "HOOK-ENV: dumpdir=$dumpdir;storeid=$storeid\n";

        #Call s3cleanup at job end
        if ($phase eq 'job-end') {
                system ("/root/ $bucket \"$retain days\"");
#For backup-based phases
} elsif ($phase eq 'backup-start' || 
         $phase eq 'backup-end' ||
         $phase eq 'backup-abort' || 
         $phase eq 'log-end' || 
         $phase eq 'pre-stop' ||
         $phase eq 'pre-restart' ||
         $phase eq 'post-restart') {

        #Data available to backup-based phases
        my $mode = shift; # stop/suspend/snapshot

        my $vmid = shift;

        my $vmtype = $ENV{VMTYPE}; # lxc/qemu

        my $dumpdir = $ENV{DUMPDIR};

        my $storeid = $ENV{STOREID};

        my $hostname = $ENV{HOSTNAME};

        my $tarfile = $ENV{TARGET};

        my $logfile = $ENV{LOGFILE}; 

        #Uncomment this to print environment variables
        #print "HOOK-ENV: vmtype=$vmtype;dumpdir=$dumpdir;storeid=$storeid;hostname=$hostname;tarfile=$tarfile;logfile=$logfile\n";

        # During backup-end, copy the target file to S3 and delete the original on the system
        if ($phase eq 'backup-end') {
                #S3 put
                my $result = system ("s3cmd put $tarfile s3://$bucket/");
                #rm original
                system ("rm $tarfile");
                #Die of error returned
                if($result != 0) {
                        die "upload backup failed";

        # During log-end, copy the log file to S3 and delete the original on the system (same as target file)
        if ($phase eq 'log-end') {
                my $result = system ("s3cmd put $logfile s3://$bucket/");
                system ("rm $logfile");
                if($result != 0) {
                        die "upload logfile failed";
#Otherwise, phase is unknown
} else {

        die "got unknown phase '$phase'";


exit (0);