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Category: Back To Basics

  • Linux – Configure iSCSI Initiator

    This blog is not to explain what is iSCSI but rather a reference to steps which an administrator should follow for configuring iSCSI on their Linux host (CentOS in my case)

    Prerequisites

    1. Make sure Linux host has IP connectivity to storage appliance which is acting as iSCSI target
    2. Storage appliance has iSCSI configured and service is running

    Steps

    Install iSCSI initiator on Linux host. Below is the example 

    # yum install iscsi-initiator-utils
Loaded plugins: ulninfo
Resolving Dependencies
--> Running transaction check
---> Package iscsi-initiator-utils.x86_64 0:6.2.0.874-11.0.1.el7 will be installed
--> Processing Dependency: iscsi-initiator-utils-iscsiuio >= 6.2.0.874-11.0.1.el7 for package: iscsi-initiator-utils-6.2.0.874-11.0.1.el7.x86_64
--> Running transaction check
---> Package iscsi-initiator-utils-iscsiuio.x86_64 0:6.2.0.874-11.0.1.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=======================================================================================================================================================
 Package                                          Arch                     Version                                  Repository                    Size
=======================================================================================================================================================
Installing:
 iscsi-initiator-utils                            x86_64                   6.2.0.874-11.0.1.el7                     ol7_latest                   428 k
Installing for dependencies:
 iscsi-initiator-utils-iscsiuio                   x86_64                   6.2.0.874-11.0.1.el7                     ol7_latest                    93 k

Transaction Summary
=======================================================================================================================================================
Install  1 Package (+1 Dependent package)

Total download size: 521 k
Installed size: 2.6 M
Is this ok [y/d/N]: y
Downloading packages:
(1/2): iscsi-initiator-utils-6.2.0.874-11.0.1.el7.x86_64.rpm                                                                    | 428 kB  00:00:00
(2/2): iscsi-initiator-utils-iscsiuio-6.2.0.874-11.0.1.el7.x86_64.rpm                                                           |  93 kB  00:00:00
-------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                  1.1 MB/s | 521 kB  00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : iscsi-initiator-utils-iscsiuio-6.2.0.874-11.0.1.el7.x86_64                                                                          1/2
  Installing : iscsi-initiator-utils-6.2.0.874-11.0.1.el7.x86_64                                                                                   2/2
  Verifying  : iscsi-initiator-utils-6.2.0.874-11.0.1.el7.x86_64                                                                                   1/2
  Verifying  : iscsi-initiator-utils-iscsiuio-6.2.0.874-11.0.1.el7.x86_64                                                                          2/2

Installed:
  iscsi-initiator-utils.x86_64 0:6.2.0.874-11.0.1.el7

Dependency Installed:
  iscsi-initiator-utils-iscsiuio.x86_64 0:6.2.0.874-11.0.1.el7

Complete!

    Once iSCSI package is installed then edit the iSCSI configuration file and enable node.startup = automatic. You will need to find node.startup in the config file and remove the # from start of the line. This will make sure that iSCSI is logging to target automatically on startup

    vi /etc/iscsi/iscsid.conf

node.startup = automatic

    Now configure the iSCSI service to start automatically. Run below command 

    # systemctl enable iscsid
Created symlink from /etc/systemd/system/multi-user.target.wants/iscsid.service to /usr/lib/systemd/system/iscsid.service.

    Start iSCSI service

    # systemctl start iscsid

    Now at this point you’ve iSCSI enabled on your Linux server. If you want to view iSCSI initiator name of your server then run below command. Note that in most cases iSCSI initiator name will reflect into logged in initiators on your storage appliance in some cases you’ll need to provide the initiator name.

    # cat /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.1988-12.com.oracle:b0ed4f9c9b9d

    Now let’s discover iSCSI target nodes using your storage system iSCSI IP address. 

    # iscsiadm -m discovery -t st -p 172.16.1.11
172.16.1.11:3260,2 iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2
172.16.1.12:3260,1 iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2

    You can run below commands to list discovered iSCSI nodes

    # iscsiadm -m node
172.16.1.11:3260,2 iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2
172.16.1.12:3260,1 iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2

or 

# ls /var/lib/iscsi/send_targets
172.16.1.11,3260

# ls /var/lib/iscsi/nodes
iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2
iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2

    Once iSCSI nodes are discovered you can run below command to login into iSCSI target

    # iscsiadm -m node --targetname "iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2" --portal "172.16.1.11:3260" --login
Logging in to [iface: default, target: iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2, portal: 172.16.1.11,3260] (multiple)
Login to [iface: default, target: iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2, portal: 172.16.1.11,3260] successful.

# iscsiadm -m node --targetname "iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2" --portal "172.16.1.12:3260" --login
Logging in to [iface: default, target: iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2, portal: 172.16.1.12,3260] (multiple)
Login to [iface: default, target: iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2, portal: 172.16.1.12,3260] successful.

    At this stage you’ve Linux host configured as iSCSI initiator and logged in successfully to target storage. Now you can ask storage admin to create LUNs and assign to Linux host.

    Once LUNs are assigned to Linux host you can run below command to scan new devices

    # iscsiadm -m session --rescan
Rescanning session [sid: 1, target: iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.a2, portal: 172.16.1.11,3260]
Rescanning session [sid: 2, target: iqn.1992-04.com.emc:cx.asfnsdbgfkdjfgdk.b2, portal: 172.16.1.12,3260]

    You can view new devices using fdisk -l or multipath -l command

  • Ansible Master – Enabling SSH Key Based Authentication

    Ansible Master – Enabling SSH Key Based Authentication

    This section seems pretty straight-forward but is the must for all the Ansible deployments.

    Follow below steps to get through the password maze in Ansible environments

    Firstly we will need to generate the SSH authentication keys. This needs to be done on the server from which you want to login to other hosts. In my case it’s Ansible master server.

    Generate your key – Run the ssh-keygen command (as below). By default system will create and store the SSH key into /root/.ssh/id_rsa, which you can change. Passphrase is optional and you can leave it blank.

    Note that if you already have generated the SSH key you have option to overwrite the same, but make sure that earlier key is not used anywhere for authentication. Below example shows option to replace existing SSH keys

    [root@ansible-master ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
/root/.ssh/id_rsa already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:D52Rvc2F7JMlbikpj7G96Ys3bSLRUz4tNmsfNP4E2Vg root@ansible-master
The key's randomart image is:
+---[RSA 2048]----+
|                 |
|           o . . |
|          o . + E|
|         . o B.@ |
|        S =.+o&+.|
|         o.BooOoo|
|          +.o+ B.|
|          ..+o=.o|
|          .+=* .o|
+----[SHA256]-----+

    If you want to use existing keys then you can simply read the existing key which is saved in the file. Below is the example of the reading existing public key

    [root@ansible-master ~]# cat /root/.ssh/id_rsa.pub
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDDoN5+wFiV3Nold4Y7KDGkvIGBqulvdDxDm3qPj7SGsHsnEZKKxbQtO2QJNDJW2tXhLLDxY7vnyQ3xiL0bXbUTkeHHANFY7yZnMH4LH1k51yAkgDdVzKYUdvVJ81qRmYaJUJnLCsKvZMFmg7/KzecuA1QU8WVDLCH02HiRsmqVPaykcR2EOKCgX7i92Q/khZycR66GvoKcVwU9LuDLlADQt9GTaFDFiXPITNayvXkWvL7bwe9arqMCJzmEpvveglJI+vLvh5793yxrszTScTuMpjvpp4Nz5Tk0NSvQqo73yiHAsFF6M7l2hnVskyj3cAOL1dzxmopC/E1qd3DrWSOX root@ansible-master

    Once you have generated the SSH key next step is to add the key into target system.

    For copying the SSH keys into target system simply follow below process.

    [root@ansible-master ~]# ssh-copy-id root@192.168.1.101
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
The authenticity of host '192.168.1.101 (192.168.1.101)' can't be established.
ECDSA key fingerprint is SHA256:qnOPcE09JqKALwLLaL+SqNMy2oubvhF/EevGCcK9S9A.
ECDSA key fingerprint is MD5:4d:65:b7:e0:e8:09:41:a8:f9:4c:2d:b6:47:55:b2:09.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@192.168.1.101's password:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'root@192.168.1.101'"
and check to make sure that only the key(s) you wanted were added.

    You’ll notice in the command output that this process has added the key into the target system. Note that 192.168.1.101 in above example is target system in which I wanted Ansible master to login without username and password.

    Once the SSH keys are added into the target system now you can try SSH into the target system and it won’t ask for password anymore.

    [root@ansible-master ~]# ssh root@192.168.1.101
Last login: Tue Nov 26 09:01:16 2019 from gateway
[root@target-system ~]#

    Hope this saves time for many of us.