Booting SystemRescueCd from the network using NBD devices

richard · 20 Feb 2010, 16:51

Hi,

Well I work with this solution for LTSP servers but also thinclients made with debian... It didn't consume a lot of memory and it light for the network.

Tree files are added in the intrd (but present in the squashfs file) :
usr/sbin/nbd-client
lib/modules/2.6.31.12-std135/kernel/drivers/block/nbd.ko

The MY_HWOPTS variable's was modified in the etc/initrd.defaults file :

Code:

...
MY_HWOPTS='modules pata sata scsi usb firewire dmraid mdadm fs net nbd'
...

Create the etc/modules/nbd file
contain only "nbd"

The modifications of init script in the intram

Code:

455a456,473
> # connect the NBD device
> sysresccd_nbdboot()
> {
>    REAL_ROOT="nbd"
>    NBD_DEVICE="/dev/nbd0"
> 
>         good_msg 'Executing nbd-client /dev/nbd0 to access nbd root'
>    NBD_SERVER=$(echo "${NBD_ROOT}" | sed 's/:.*//')
>    NBD_PORT=$(echo "${NBD_ROOT}" | sed 's/.*://')
> 
>    # connect nbd device
>    /usr/sbin/nbd-client "${NBD_SERVER}" "${NBD_PORT}" "${NBD_DEVICE}" -persist
> 
>    # mount rofs
>    mkdir /rofs
>    mount ${NBD_DEVICE} /rofs
> }
> 
489a508
> NBD_ROOT=''
574a594,598
>       nbdroot\=*)
>          NBD_ROOT=`parse_opt "${x}"`
>          LOADNET='1'
>          CDROOT='0'
>       ;;
758a783,788
> # ---- don't load the nbd modules which is time consuming if nbd not involved
> if [ -z "${NBD_ROOT}" ]
> then
>    rm -f /etc/modules/nbd
> fi
> 
786c816
< if [ -n "${NETBOOT}" ]
---
> if [ -n "${NETBOOT}" ] || [ -n "${NBD_ROOT}" ]
1130a1164,1169
> # create the nbd device on demand
> if [ -x /usr/sbin/nbd-client ] && [ -n "${NBD_ROOT}" ]
> then
>    sysresccd_nbdboot # boot with nbd device
> fi
> 
1220c1259
<       elif [ -b "${REAL_ROOT}" ] || [ "${REAL_ROOT}" = "http" ] || [ "${REAL_ROOT}" = "tftp" ]
---
>       elif [ -b "${REAL_ROOT}" ] || [ "${REAL_ROOT}" = "http" ] || [ "${REAL_ROOT}" = "tftp" ] || [ "${REAL_ROOT}" = "nbd" ]
1231c1270
<    if [ "${CDROOT}" = '1' ] && [ "${got_good_root}" = '1' ]
---
>    if [ "${CDROOT}" = '1' ] && [ "${got_good_root}" = '1' ] || [ "${REAL_ROOT}" = "nbd" ]
1507a1547,1554
> # If cdroot is unset determine and nbdboot is define try to mount root
> if [ ${CDROOT} = '0' ] && [ "${REAL_ROOT}" = "nbd" ]
> then
>    mkdir /rwfs
>    mount -t tmpfs tmpfs /rwfs
>    mount -t aufs -o dirs=/rwfs=rw:/rofs=ro aufs ${NEW_ROOT}
> fi
> 
ltsp-server:/var/lib/tftpboot/sysrcd/initram_custom# diff -cB init.ORI init 
*** init.ORI   2010-02-20 16:38:34.000000000 +0100
--- init   2010-02-20 18:13:28.000000000 +0100
***************
*** 453,458 ****
--- 453,476 ----
     echo "netconfig1: ${ipcmd_add} --> ${res}"
  }
  
+ # connect the NBD device
+ sysresccd_nbdboot()
+ {
+    REAL_ROOT="nbd"
+    NBD_DEVICE="/dev/nbd0"
+ 
+         good_msg 'Executing nbd-client /dev/nbd0 to access nbd root'
+    NBD_SERVER=$(echo "${NBD_ROOT}" | sed 's/:.*//')
+    NBD_PORT=$(echo "${NBD_ROOT}" | sed 's/.*://')
+ 
+    # connect nbd device
+    /usr/sbin/nbd-client "${NBD_SERVER}" "${NBD_PORT}" "${NBD_DEVICE}" -persist
+ 
+    # mount rofs
+    mkdir /rofs
+    mount ${NBD_DEVICE} /rofs
+ }
+ 
  # Clean input/output
  exec >${CONSOLE} <${CONSOLE} 2>&1
  [ ! -f /dev/urandom ] && busybox mknod /dev/urandom c 1 9 2>/dev/null
***************
*** 487,492 ****
--- 505,511 ----
  
  CMDLINE="$(cat /proc/cmdline)"
  CDROOT='1'
+ NBD_ROOT=''
  REAL_ROOT=''
  SETKMAP=''
  MINISHELL=''
***************
*** 572,577 ****
--- 591,601 ----
           NETBOOT=`parse_opt "${x}"`
           LOADNET='1'
        ;;
+       nbdroot\=*)
+          NBD_ROOT=`parse_opt "${x}"`
+          LOADNET='1'
+          CDROOT='0'
+       ;;
        subdir\=*)
           SUBDIR=`parse_opt "${x}"`
        ;;
***************
*** 756,761 ****
--- 780,791 ----
     rm -f /etc/modules/net
  fi
  
+ # ---- don't load the nbd modules which is time consuming if nbd not involved
+ if [ -z "${NBD_ROOT}" ]
+ then
+    rm -f /etc/modules/nbd
+ fi
+ 
  # ---- load modules listed in MY_HWOPTS if /lib/modules exists
  if [ -d '/lib/modules' ]
  then
***************
*** 783,789 ****
  good_msg "Performing the network configuration..."
  
  # ---- force dhcp if booting via pxe and no static configuration specified
! if [ -n "${NETBOOT}" ]
  then
     if ! cat /proc/cmdline | busybox grep -q -E 'eth[x0-9]{1,2}=[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
     then
--- 813,819 ----
  good_msg "Performing the network configuration..."
  
  # ---- force dhcp if booting via pxe and no static configuration specified
! if [ -n "${NETBOOT}" ] || [ -n "${NBD_ROOT}" ]
  then
     if ! cat /proc/cmdline | busybox grep -q -E 'eth[x0-9]{1,2}=[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
     then
***************
*** 1128,1133 ****
--- 1161,1172 ----
     /bin/lvm vgchange -ay
  fi
  
+ # create the nbd device on demand
+ if [ -x /usr/sbin/nbd-client ] && [ -n "${NBD_ROOT}" ]
+ then
+    sysresccd_nbdboot # boot with nbd device
+ fi
+ 
  while true
  do
     while [ "${got_good_root}" != '1' ]
***************
*** 1217,1223 ****
           echo -n 'boot() :: '
           read REAL_ROOT
           got_good_root=0
!       elif [ -b "${REAL_ROOT}" ] || [ "${REAL_ROOT}" = "http" ] || [ "${REAL_ROOT}" = "tftp" ]
        then
           got_good_root=1
        else
--- 1256,1262 ----
           echo -n 'boot() :: '
           read REAL_ROOT
           got_good_root=0
!       elif [ -b "${REAL_ROOT}" ] || [ "${REAL_ROOT}" = "http" ] || [ "${REAL_ROOT}" = "tftp" ] || [ "${REAL_ROOT}" = "nbd" ]
        then
           got_good_root=1
        else
***************
*** 1228,1234 ****
        fi
     done
  
!    if [ "${CDROOT}" = '1' ] && [ "${got_good_root}" = '1' ]
     then
        # CD already mounted; no further checks necessary
        break
--- 1267,1273 ----
        fi
     done
  
!    if [ "${CDROOT}" = '1' ] && [ "${got_good_root}" = '1' ] || [ "${REAL_ROOT}" = "nbd" ]
     then
        # CD already mounted; no further checks necessary
        break
***************
*** 1505,1510 ****
--- 1544,1557 ----
     fi
  fi
  
+ # If cdroot is unset determine and nbdboot is define try to mount root
+ if [ ${CDROOT} = '0' ] && [ "${REAL_ROOT}" = "nbd" ]
+ then
+    mkdir /rwfs
+    mount -t tmpfs tmpfs /rwfs
+    mount -t aufs -o dirs=/rwfs=rw:/rofs=ro aufs ${NEW_ROOT}
+ fi
+ 
  verbose_kmsg
  
  # ------------------------------- chroot -------------------------------

So, for the nbd-server you can use a file ...

Code:

# /etc/nbd-server/config
[generic]
   user = nbd
   group = nbd
   listenaddr = 172.16.0.1
[partimage]
   exportname = /mnt/cdrom/sysrcd.dat
   port = 2000

... or a command

Code:

root@sysresccd /root % nbd-server 2000 /mnt/cdrom/sysrcd.dat

In the default file of /tftpboot/pxelinux.cfg/default you can find :

Code:

default rescuecd
append initrd=initram-nbd.igz  setkmap=fr nbdroot=172.16.0.1:2000

Copy necessary files to /tftpboot directory :
/mnt/cdrom/isolinux/rescuecd
/mnt/cdrom/isolinux/initram-nbd.igz

Configure and start the dhcp and tftp server

Start your thins-clients

@+

Booting SystemRescueCd from the network using NBD devices

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