rhel 7

Network Interface Name in rhel7

Anyone who has installed rhel7 knows how annoying it is to check you network and not see eth0.  Perhaps it is just me then…  Regardless here are instructions on how to change it:

First you need to know the name of the network adapter in use, you can look in /etc/sysconfig/network-scripts/ifcfg-eno##### or run this command:

# ip addr show
Now you need to do the following:
vim /etc/sysconfig/grub
add “net.ifnames=0 biosdevname=0″ to the end of the line beginning with: GRUB_CMDLINE_LINUX, for example:
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet net.ifnames=0 biosdevname=0"
Now you need to regenerate the GRUB configuration with the updated kernel parameters:
# grub2-mkconfig -o /boot/grub2/grub.cfg
Now you need to change the ‘eno##” named network scripts you identified above:
# cp -p /etc/sysconfig/network-scripts/ifcfg-eno16780032 /etc/sysconfig/network-scripts/ifcfg-eth0

Next edit the newly copied network script to change any reference to the eno### to eth0, for example:

sed -i -e 's/eno16780032/eth0/g' /etc/sysconfig/network-scripts/ifcfg-eth0

Now reboot:

# shutdown -r now

After system reboot your network interface shall be called eth0 and all will be right in the world again…

Hat tip to Angelo for most of the leg work.

yum Invalid System Credential error

I ran across the following yum error after migrating a system from being a client of Satellite 5.6 to Satellite 6.1.  First here is the error:

# yum update
Loaded plugins: package_upload, priorities, rhnplugin, search-disabled-repos, security, subscription-manager
There was an error communicating with RHN.
RHN Satellite or RHN Classic support will be disabled.

Error Message:
    Please run rhn_register as root on this client
Error Class Code: 9
Error Class Info: Invalid System Credentials.
     An error has occurred while processing your request. If this problem
     persists please enter a bug report at bugzilla.redhat.com.
     If you choose to submit the bug report, please be sure to include
     details of what you were trying to do when this error occurred and
     details on how to reproduce this problem.

Setting up Update Process
rhel-6-server-rpms                                                                                                                                                            | 2.0 kB     00:00     
rhel-6-server-satellite-tools-6.1-rpms                                                                                                                                        | 2.1 kB     00:00     
No Packages marked for Update
This left me scratching my head for a few and a quick search didn’t produce much so I thought I should document this for prosperity.
The problem was with the contents of the file /etc/yum/pluginconf.d/rhnplugin.conf
Part of my transition is running this command:
sed -i -e 's/enabled=1/enabled=0/g' /etc/yum/pluginconf.d/rhnplugin.conf
The problem was unlike all of my other systems, this file must have been edited because instead of containing “enabled=1” it contained “enabled = 1”
To correct that I modified my sed command to ignore white space:
sed -i -e 's/enabled\s*=\s*1/enabled=0/g' /etc/yum/pluginconf.d/rhnplugin.conf

More details can be found using the yum.conf man page.

Hope that is helpful.


systemd commands, hints and cheatsheet

List all running services

# systemctl

Start/stop or enable/disable services

Activates a service immediately:

# systemctl start foo.service

Deactivates a service immediately:

# systemctl stop foo.service

Restarts a service:

# systemctl restart foo.service

Shows status of a service including whether it is running or not:

# systemctl status foo.service

Enables a service to be started on bootup:

# systemctl enable foo.service

Disables a service to not start during bootup:

# systemctl disable foo.service

Check whether a service is already enabled or not:

# systemctl is-enabled foo.service; echo $?

0 indicates that it is enabled. 1 indicates that it is disabled

How do I change the runlevel?

systemd has the concept of targets which is a more flexible replacement for runlevels in sysvinit.

Run level 3 is emulated by multi-user.target. Run level 5 is emulated by graphical.target. runlevel3.target is a symbolic link to multi-user.target and runlevel5.target is a symbolic link to graphical.target.

You can switch to ‘runlevel 3′ by running

# systemctl isolate multi-user.target (or) systemctl isolate runlevel3.target

You can switch to ‘runlevel 5′ by running

# systemctl isolate graphical.target (or) systemctl isolate runlevel5.target

How do I change the default runlevel?

systemd uses symlinks to point to the default runlevel. You have to delete the existing symlink first before creating a new one

# rm /etc/systemd/system/default.target

Switch to runlevel 3 by default

# ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target

Switch to runlevel 5 by default

# ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target

systemd does not use /etc/inittab file.

List the current run level

runlevel command still works with systemd. You can continue using that however runlevels is a legacy concept in systemd and is emulated via ‘targets’ and multiple targets can be active at the same time. So the equivalent in systemd terms is

# systemctl list-units --type=target

Powering off the machine

You can use

# poweroff

Some more possibilities are: halt -p, init 0, shutdown -P now

Note that halt used to work the same as poweroff in previous Fedora releases, but systemd distinguishes between the two, so halt without parameters now does exactly what it says – it merely stops the system without turning it off.


Service vs. systemd

# service NetworkManager stop


# systemctl stop NetworkManager.service

Chkconfig vs. systemd

# chkconfig NetworkManager off


# systemctl disable NetworkManager.service


systemd has a built-in readahead implementation is not enabled on upgrades. It should improve bootup speed but your mileage may vary depending on your hardware. To enable readahead:

# systemctl enable systemd-readahead-collect.service
# systemctl enable systemd-readahead-replay.service

SystemD cheatsheet

service foobar start systemctl start foobar.service Used to start a service (not reboot persistent)
service foobar stop systemctl stop foobar.service Used to stop a service (not reboot persistent)
service foobar restart systemctl restart foobar.service Used to stop and then start a service
service foobar reload systemctl reload foobar.service When supported, reloads the config file without interrupting pending operations.
service foobar condrestart systemctl condrestart foobar.service Restarts if the service is already running.
service foobar status systemctl status foobar.service Tells whether a service is currently running.
ls /etc/rc.d/init.d/ ls /lib/systemd/system/*.service /etc/systemd/system/*.service Used to list the services that can be started or stopped
chkconfig foobar on systemctl enable foobar.service Turn the service on, for start at next boot, or other trigger.
chkconfig foobar off systemctl disable foobar.service Turn the service off for the next reboot, or any other trigger.
chkconfig foobar systemctl is-enabled foobar.service Used to check whether a service is configured to start or not in the current environment.
chkconfig foobar –list ls /etc/systemd/system/*.wants/foobar.service Used to list what levels this service is configured on or off
chkconfig foobar –add Not needed, no equivalent.


Linux readahead: less tricks for more

Password Recovery in Redhat 7

Forgot your password on your rhel7 server? Well there are some differences to process from rhel6. Here is how you do it.

With SELinux and systemd in the mix we have to deal with that. Here is the procedure of what needs to be done in order to recover a forgotten root password on Redhat 7 Linux:

Edit the GRUB2 boot menu and enter user single mode
Remount / partition to allow read and write
Reset the actual root password
Set entire system for SElinux relabeling after first reboot
Reboot the system from single mode

Now that we understand the procedure we can proceed with Redhat 7 password recovery.

1. Edit GRUB2 boot menu

Start your system and once you see your GRUB2 boot menu use ‘e’ key to edit your default boot item. Usually it is the first line. Once you hit the ‘e’ key, scroll down and locate a line with ‘rhgb quiet’ keywords:

locate-line-grub2-boot-menu-rhel7-linuxMove to end of the line with CTRL+E then cursor to “rhgb quiet" keywords and replace them with “init=/bin/bash" as show below:


Once you edit the boot line as show above press “CTRL + x" to start booting your RHEL 7 system into a single mode. At the end of the system boot you will enter a single mode.


2. Read&Write root partition remount

Once you enter a single your root partition is mounted as Read Only ro. You ca confirm it with the following command:

# mount | grep root

In order to mount our partition with Read/Write flag we use mount with a remount option as follows:

# mount -o remount,rw /

Next, confirm that the root file system is mounted Read/Write rw:

# mount | grep root

3. Change root’s password

Still in the single mode we can proceed with the actual root password recovery. To do this we use passwd command:

# passwd

You will need to enter your password twice.

4. SELinux relabeling

The additional step which needs to be taken on SELinux enables Linux system is to relabel SELinux context. If this step is ommited you will not be able to login with your new root password. The following command will ensure that the SELinux context for entire system is relabeled after reboot:

# touch /.autorelabel

5. Reboot System

The final step when resetting your lost root password on RHEL 7 linux system is to reboot. This can be done with a following command:

# exec /sbin/init

After reboot you will be able to use your new root password.

Rhel6, Rhel7 Comparison

Moving from Redhat 6 to Redhat 7.  There are a *lot* of differences to get use to.  It is like having a friend come over and rearrange your entire house, including all the closets and cupboards!! You know it is your house, you just can’t seem to find any of your stuff!

Features RHEL 7 RHEL 6
Default File System XFS EXT4
Kernel Version 3.10.x-x kernel 2.6.x-x Kernel
Kernel Code Name Maipo Santiago
General Availability Date of First Major Release 2014-06-09 (Kernel Version 3.10.0-123) 2010-11-09 (Kernel Version 2.6.32-71)
First Process systemd (process ID 1) init (process ID 1)
Runlevel runlevels are called as “targets” as shown below:runlevel0.target -> poweroff.target

runlevel1.target -> rescue.target

runlevel2.target -> multi-user.target

runlevel3.target -> multi-user.target

runlevel4.target -> multi-user.target

runlevel5.target -> graphical.target

runlevel6.target -> reboot.target

/etc/systemd/system/default.target (this by default is linked to the multi-user target)

Traditional runlevels defined :runlevel 0

runlevel 1

runlevel 2

runlevel 3

runlevel 4

runlevel 5

runlevel 6

and the default runlevel would be defined in /etc/inittab file.


Host Name Change with the move to systemd, the hostname variable is defined in /etc/hostname. In Red Hat Enterprise Linux 6, the hostname variable was defined in the /etc/sysconfig/network configuration file.
Change In UID Allocation By default any new users created would get UIDs assigned starting from 1000.This could be changed in /etc/login.defs if required. Default UID assigned to users would start from 500.
This could be changed in /etc/login.defs if required.
Max Supported File Size Maximum (individual) file size = 500TBMaximum filesystem size = 500TB(This maximum file size is only on 64-bit machines. Red Hat Enterprise Linux does not support XFS on 32-bit machines.) Maximum (individual) file size = 16TBMaximum filesystem size = 16TB(This maximum file size is based on a 64-bit machine. On a 32-bit machine, the maximum files size is 8TB.)
File System Check “xfs_repair”XFS does not run a file system check at boot time. “e2fsck”File system check would gets executed at boot time.
Differences Between xfs_repair & e2fsck “xfs_repair”- Inode and inode blockmap (addressing) checks.- Inode allocation map checks.

– Inode size checks.

– Directory checks.

– Pathname checks.

– Link count checks.

– Freemap checks.

– Super block checks.

“e2fsck”- Inode, block, and size checks.- Directory structure checks.

– Directory connectivity checks.

– Reference count checks.

– Group summary info checks.

Difference Between xfs_growfs & resize2fs “xfs_growfs”xfs_growfs takes mount point as arguments. “resize2fs”resize2fs takes logical volume name as arguments.
Change In File System Structure /bin, /sbin, /lib, and /lib64 are now nested under /usr. /bin, /sbin, /lib, and /lib64 are usually under /
Boot Loader GRUB 2Supports GPT, additional firmware types, including BIOS, EFI and OpenFirmwar. Ability to boot on various file systems (xfs, ext4, ntfs, hfs+, raid, etc) GRUB 0.97
KDUMP Supports kdump on large memory based systems up to 3 TB Kdump doesn’t work properly with large RAM based systems.
System & Service Manager “Systemd”systemd is compatible with the SysV and Linux Standard Base init scripts it replaces. Upstart
Enable/Start Service the systemctl command replaces service and chkconfig.- Start Service : “systemctl start nfs-server.service”.

– Enable Service : To enable the service (example: nfs service ) to start automatically on boot : “systemctl enable nfs-server.service”.

Although one can still use the service and chkconfig commands to start/stop and enable/disable services, respectively, they

are not 100% compatible with the RHEL 7 systemctl command (according to redhat).

Using “service” command and “chkconfig” commands.- Start Service : “service start nfs” OR “/etc/init.d/nfs start”

– Enable Service : To start with specific runlevel : “chkconfig –level 3 5 nfs on”

Default Firewall “Firewalld (Dynamic Firewall)”The built-in configuration is located under the /usr/lib/firewalld directory. The configuration that you can customize is under the /etc/firewalld directory. It is not possible to use Firewalld and Iptables at the same time. But it is still possible to disable Firewalld and use Iptables as before. Iptables
Network Bonding “Team Driver”-/etc/sysconfig/network-scripts/ifcfg-team0

– DEVICE=”team0”



– DEVICE=”bond0”

Network Time Synchronization Using Chrony suite (faster time sync compared with ntpd) Using ntpd
NFS NFS4.1NFSv2 is no longer supported. Red Hat Enterprise Linux 7 supports NFSv3, NFSv4.0, and NVSv4.1 clients. NFS4
Cluster Resource Manager Pacemaker Rgmanager
Load Balancer Technology Keepalived and HAProxy Piranha
Desktop/GUI Interface GNOME3 and KDE 4.10 GNOME2
Default Database MariaDB is the default implementation of MySQL MySQL
Managing Temporary Files systemd-tmpfiles (more structured, and configurable, method to manage tmp files and directories). Using “tmpwatch”
References :-

To reboot or not to reboot?

You have patches to apply, we all know that if there are kernel patches that you need to (or at least should) restart/reboot the server.  But what about other packages?  There are a few non-kernel patches which can cause havoc if you spply them and do not reboot the server.  The biggest package that most people miss are libraries, specifically libraries used by the system, like glibc.  When the system is running it loads the libraries it needs into memory, updating does not force a reload of those libraries. Therefore after patching you will have the old version in memory and the new version on disk.  When a new subroutine or kernel process is called it will load the new version into memory, this is where the fun can start.  I say fun because you can see some really strange behavior.  Perhaps you have and in frustration rebooted, problem solved but you are perplexed, well now you know.

Since I deal mostly with Redhat these days here are the packages that require/highly recommend a reboot of the server.  (Caveat: If you can reload what is in memory you do not need to reboot.  This is what we do with services like tomcat or apache after a patch and that removes the old packages from memory and loads the new.)

While we all want to avoid interruptions to system uptime, when updating these packages a reboot is required.  Remember to use your own discretion as this list is provided as an informational guide only.  Redhat could introduce changes that increase or decrease this list.  You may be using packages not considered or functionality not examined.

Red Hat Enterprise Linux 5:

  • kernel
  • kernel-smp
  • kernel-PAE
  • kernel-xen
  • glibc
  • hal

Red Hat Enterprise Linux 6:

  • kernel
  • *-firmware-*
  • glibc
  • hal

Red Hat Enterprise Linux 7:

  • kernel
  • glibc
  • linux-firmware
  • systemd
  • udev

Remember if you don’t have to reboot you should restart the updated service.  Good Luck.