You'll need:

• An iSCSI-enabled kernel (or kernel modules). This is standard in kernels >= 2.6.18.
• Userland tools from the "open-iscsi" package. Probably not installed by default, so install with your favorite package manager (or tarball, if that's how you roll).

There are two halves to the iSCSI software initiator:

1. Kernel parts, which do "read block", "write block"
2. Userland parts: administration, login, logout, etc.

Basically, the process of mounting a LUN works as follows:

1. In userland, "discover" the target & lun, save info to a config file.
2. In userland, "login" to target, which makes the kernel create a /dev/sd? device for the LUN(s)
3. Mess with device as normal.

• Install package "open-iscsi" (userland tools) from your distributions package manager. In Ubuntu:

$ sudo apt-get install open-iscsi

• Check/set iSCSI initiator name. This may be in '/etc/initiatorname.iscsi' or '/etc/iscsi/initiatorname.iscsi'

$ sudo YourEditorOfChoice /etc/iscsi/initiatorname.iscsi

• Load the modules & start the iscsid service. Your package manager may have done this for you, but make sure.

In RedHat:

$ sudo service open-iscsi start

Elsewhere:

$ sudo /etc/init.d/open-iscsi start

This makes dmesg say:

Loading iSCSI transport class v2.0-724.
iscsi: registered transport (tcp)
iscsi: registered transport (iser)

• Associate given initiator with an iGroup and LUN on the filer.

• Perform iSCSI discovery to populate your config files:

$ iscsiadm -m discovery -t sendtargets -p 10.60.118.14:3260
10.60.118.14:3260,1001 iqn.1992-08.com.netapp:sn.101166881

• "Log in" to the filer to attach the LUN:

$ iscsiadm -m node -T iqn.1992-08.com.netapp:sn.101166881 -p 10.60.118.14:3260 -l

This makes dmesg say:

scsi4 : iSCSI Initiator over TCP/IP
scsi 4:0:0:0: Direct-Access     NETAPP   LUN              0.2  PQ: 0 ANSI: 4
SCSI device sdb: 16777216 512-byte hdwr sectors (8590 MB)
sdb: Write Protect is off
sdb: Mode Sense: bd 00 00 08
SCSI device sdb: write cache: disabled, read cache: enabled, doesn't support DPO or FUA
SCSI device sdb: 16777216 512-byte hdwr sectors (8590 MB)
sdb: Write Protect is off
sdb: Mode Sense: bd 00 00 08
SCSI device sdb: write cache: disabled, read cache: enabled, doesn't support DPO or FUA
 sdb: sdb1 sdb2
sd 4:0:0:0: Attached scsi disk sdb
sd 4:0:0:0: Attached scsi generic sg1 type 0

• The LUN is now treated like a local SCSI drive, so we can do things like:

$ fdisk /dev/sdb
$ mount /dev/sdb2 /mnt/mylun

• Optional - make the iSCSI login occur automatically at boot:
  • First, make our LUN be attached whenever the iscsid service is started:
    • Edit /etc/iscsi/nodes/<Target_IQN>/<Target_IP_and_port>
    • Change "node.startup = manual" to "node.startup = automatic"
  • Second, make the iscsi service load at boot. For Ubuntu, run "services-admin". For RedHat, do:

$ chkconfig --level <levels> open-iscsi on