Provided by: borgbackup_1.1.15-1~ubuntu1.18.04.2_amd64 bug

NAME

       borg-serve - Start in server mode. This command is usually not used manually.

SYNOPSIS

       borg [common options] serve [options]

DESCRIPTION

       This  command  starts  a  repository  server  process.  This  command  is usually not used
       manually.

OPTIONS

       See borg-common(1) for common options of Borg commands.

   optional arguments
       --restrict-to-path PATH
              restrict repository access to PATH. Can be specified multiple times  to  allow  the
              client  access  to  several  directories.  Access to all sub-directories is granted
              implicitly; PATH doesn't need to directly point to a repository.

       --restrict-to-repository PATH
              restrict repository access. Only the repository located at PATH (no sub-directories
              are  considered) is accessible. Can be specified multiple times to allow the client
              access to several repositories. Unlike --restrict-to-path sub-directories  are  not
              accessible;  PATH  needs to directly point at a repository location. PATH may be an
              empty directory or the last element of PATH may not exist, in which case the client
              may initialize a repository there.

       --append-only
              only allow appending to repository segment files

       --storage-quota QUOTA
              Override  storage quota of the repository (e.g. 5G, 1.5T). When a new repository is
              initialized, sets the storage quota on the new  repository  as  well.  Default:  no
              quota.

EXAMPLES

       borg  serve  has  special  support  for  ssh  forced commands (see authorized_keys example
       below): it will detect that you use such a forced command and extract  the  value  of  the
       --restrict-to-path option(s).

       It  will  then parse the original command that came from the client, makes sure that it is
       also borg serve and enforce path restriction(s) as given by the forced command. That  way,
       other  options  given  by  the  client (like --info or --umask) are preserved (and are not
       fixed by the forced command).

       Environment variables (such as BORG_HOSTNAME_IS_UNIQUE) contained in the original  command
       sent  by  the  client  are not interpreted, but ignored. If BORG_XXX environment variables
       should be set on the borg serve side, then these must be set in system-specific  locations
       like /etc/environment or in the forced command itself (example below).

          # Allow an SSH keypair to only run borg, and only have access to /path/to/repo.
          # Use key options to disable unneeded and potentially dangerous SSH functionality.
          # This will help to secure an automated remote backup system.
          $ cat ~/.ssh/authorized_keys
          command="borg serve --restrict-to-path /path/to/repo",restrict ssh-rsa AAAAB3[...]

          # Set a BORG_XXX environment variable on the "borg serve" side
          $ cat ~/.ssh/authorized_keys
          command="export BORG_XXX=value; borg serve [...]",restrict ssh-rsa [...]

       NOTE:
          The  examples above use the restrict directive. This does automatically block potential
          dangerous ssh features, even when they are added in a future update. Thus, this  option
          should be preferred.

          If  you're  using openssh-server < 7.2, however, you have to explicitly specify the ssh
          features to restrict and  cannot  simply  use  the  restrict  option  as  it  has  been
          introduced         in         v7.2.         We         recommend         to         use
          no-port-forwarding,no-X11-forwarding,no-pty,no-agent-forwarding,no-user-rc   in    this
          case.

   SSH Configuration
       borg  serve's  pipes (stdin/stdout/stderr) are connected to the sshd process on the server
       side. In the event  that  the  SSH  connection  between  borg  serve  and  the  client  is
       disconnected  or  stuck  abnormally  (for example, due to a network outage), it can take a
       long time for sshd to notice the client is disconnected. In the meantime,  sshd  continues
       running,  and  as  a  result  so  does  the  borg  serve  process  holding the lock on the
       repository. This can cause subsequent borg operations on the  remote  repository  to  fail
       with the error: Failed to create/acquire the lock.

       In  order  to  avoid  this,  it  is  recommended  to  perform the following additional SSH
       configuration:

       Either in the client side's ~/.ssh/config file, or  in  the  client's  /etc/ssh/ssh_config
       file:

          Host backupserver
                  ServerAliveInterval 10
                  ServerAliveCountMax 30

       Replacing backupserver with the hostname, FQDN or IP address of the borg server.

       This  will  cause  the  client  to  send a keepalive to the server every 10 seconds. If 30
       consecutive keepalives are sent without a response (a time of 300 seconds), the ssh client
       process will be terminated, causing the borg process to terminate gracefully.

       On the server side's sshd configuration file (typically /etc/ssh/sshd_config):

          ClientAliveInterval 10
          ClientAliveCountMax 30

       This  will  cause  the  server  to send a keep alive to the client every 10 seconds. If 30
       consecutive keepalives are sent without a response (a time of 300 seconds),  the  server's
       sshd  process  will  be terminated, causing the borg serve process to terminate gracefully
       and release the lock on the repository.

       If you then run borg commands with --lock-wait 600, this gives  sufficient  time  for  the
       borg  serve  processes  to  terminate  after the SSH connection is torn down after the 300
       second wait for the keepalives to fail.

       You may, of course, modify the timeout values demonstrated above to values that suit  your
       environment and use case.

SEE ALSO

       borg-common(1)

AUTHOR

       The Borg Collective

                                            2020-12-24                              BORG-SERVE(1)