Limitations

• Command line length: 2048
• dhcp root-path: 255

See also: dracut.8

Configuration in initrd

• /conf/conf.d/*
  • command line options can override values set here

Standard

• init=<path to real init>
• root=<path to blockdevice>
  • specify e.g. /dev/sda1 or
  • /dev/disk/by-path/pci-0000:00:1f.1-scsi-0:0:1:0-part1

DHCP

• root=dhcp
  • get IP from dhcp server, root-path option from dhcp specifies root location

NFSv3

• root=[<server-ip>:]<root-dir>[:<nfs-options>]
  • mount nfs share from <server-ip>:/<root-dir>
  • if no server-ip is given, use dhcp next_server
  • nfs-options can be appended with the prefix ":" or ","
• root=dhcp
  • root-path=<server-ip>:<root-dir>[,<nfs-options>]
  • root=dhcp alone directs initrd to look at the DHCP root-path where NFS options can be specified.
• Deprecated root=/dev/nfs nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
  • kernel Documentation/filesystems/nfsroot.txt defines this method. This is supported by dracut but not recommended.

NFSv4

• root=nfs4:[<server-ip>:]<root-dir>[:<nfs-options>]
  • mount nfsv4 share from <server-ip>:/<root-dir>
  • if no server-ip is given, use dhcp next_server
  • nfs-options can be appended with the prefix ":" or ","
• root=dhcp
  • root-path=nfs4:<server-ip>:<root-dir>[,<nfs-options>]
  • root=dhcp alone directs initrd to look at the DHCP root-path where NFS options can be specified.

iSCSI

• root=iscsi:[<servername>]:[<protocol>]:[<port>]:[<LUN>]:<targetname>::
  • protocol defaults to "6", LUN defaults to "0".

       If the "servername" field is provided by BOOTP or DHCP, then that
       field is used in conjunction with other associated fields to contact
       the boot server in the Boot stage (Section 7).  However, if the
       "servername" field is not provided, then the "targetname" field is
       then used in the Discovery Service stage in conjunction with other
       associated fields.
    
      http://tools.ietf.org/html/rfc4173
    

• root=??? iscsiroot=...::
• root=??? iscsi_initiator= iscsi_target_name= iscsi_target_ip= iscsi_target_port= iscsi_target_group= iscsi_username= iscsi_password= iscsi_in_username= iscsi_in_password=::
• root=??? iscsi_firmware::

NBD

• root=nbd:<server>:<port>[:<fstype>][:<mountopts>]
  • mount nbd share from <server>
• root=dhcp
  • root-path=nbd:<server>:<port>[:<fstype>][:<mountopts>]
    
  • root=dhcp alone directs initrd to look at the DHCP root-path where NBD options can be specified.
  • This syntax is only usable in cases where you are directly mounting the volume as the rootfs.

Network

• ip=[dhcp|on|any]
  • get ip from dhcp server from all interfaces
  • If root=dhcp, loop sequentially through all interfaces (eth0, eth1, ...) and use the first with a valid DHCP root-path.
• ip=<interface>:[dhcp|on|any]
  • get ip from dhcp server on a specific interface
• ip=<client-IP-number>:<gateway-IP-number>:<netmask>:<client-hostname>:<interface>:[dhcp|on|any|]
  • explicit network configuration

Bridging

• bridge=<bridgename>:<ethname>
• If bridge is specified without parameters, then bridge=br0:eth0 is assumed.
• You may optionally configure dracut to netboot over a bridged interface. Bridges may be given any name (usually br0), and an interface (usually eth0) is permanently assigned to that bridge. dhclient and mount happens using the bridge br0 instead of eth0, but everything behaves identically.
• The usual case where you would want to netboot over a bridged interface is if you intend on running virtual machines on that netbooted machine.

Misc

• rdblacklist=<modulename>
  • TBD: do not load modulename

Debug

• rdinitdebug
  • set -x for the dracut shell
• rdbreak=[cmdline|pre-udev|pre-trigger|initqueue|pre-mount|mount|pre-pivot]
  • drop the shell on defined breakpoint
• rdudevinfo
  • set udev to loglevel info
• rdudevdebug
  • set udev to loglevel debug
• rdnetdebug
  • debug network scripts in dracut