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5 New features in RHEL 7 you should know about.

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[系统(linux) 所属分类 系统(linux) | 发布者 店小二05 | 时间 2017 | 作者 红领巾 ] 0人收藏点击收藏

With RHEL 7 RedHat has made significant changes the way linux used to work. Here we are discussingNew features in RHEL 7.

1> Firstly, RHEL7 boots up much faster than RHEL 6 and other versions.

Fast booting is one of the main new features in RHEL 7.

Yes, RHEL 7 boots up quickly which is achieved by simultaneously starting up the services which are not dependent on each other, for instance: sendmail and mariadb are not dependent on each other, so they can be started simultaneously, but until RHEL 6 if sendmail had some issues during booting , boot process would wait until sendmail failed, and then start rest of the services, this delayed booting time. With RHEL 7, RedHat is able to overcome this issue.

2> Init process is no more the main process or 1 st process or father of all process.

Init process is now replaced by systemd process. Now systemd process is 1 st process, and father of all process. Inclusion of systemd process is biggest new features in RHEL 7.

3> Starting and stopping of services with RHEL 7 has changed.

/etc/init.d/services has been changed, now to start/stop or enable any services is done using systelctl command.

To check the all services, we use “ systemctl -a ”

[[email protected] -]# systemctl -a | grep chron ime-sync.target loadedinactivedead SystemTimeSynchronized [[email protected] -]#

In the above example, we have grepped for chron service, without grep “ systemctl a ” would show all the services from active, inactive and loaded.

Note: Chronyd is a new service, which would replace ntp. However with RHEL 7 the service is still not matured enough, hence RedHat has given ntp also with this release.

To startup any service at boot up(I am not using runlevel here, because run level has also changed) we need to execute the command:-

systemctlenablechronyd.service For disabling the service use command systemctldisablechronyd.service

Note: We don’t need to remember the complete service name, TAB key works here after systelctl enable.

Enable/disable will start the service at the bootup, and not on that moment. To start/stop/restart/status the service

systemctlstartchronyd.service [[email protected] -]#systemctl start chronyd.service [[email protected] -]# systemctl status chronyd.service chronyd.service - NTPclient/carver Loaded: loadedWusr/lib/systemd/system/chronyd.service; enabled) Active: active (running) sinceFri 2015-06-12 22:22:32 PDT; 7s ago Process: 3482 ExecStartPost=/usr/libexec/chrony-helperadd-dhclient-servers (code=exited, status=0/SUCCESS) Process: 3479 ExecStart=/usr/sbin/chronyd -u chrony $OPTIONS (code=exited, status=0/SUCCESS) MainPID: 3481 (chronyd) CGroup: /system.slice/chronyd.service L-3481 /usr/sbin/chronyd -u chrony Jun 12 22:22:32 hostlsystemd[1]: StartingNTPclient/server... Jun 12 22:22:32 hostlchronyd[3481]: chronydversion 1.29.1 starting Jun 12 22:22:32 hostlchronyd[3481]: Linuxkernelmajor=3 minor=10 patch=0 Jun 12 22:22:32 hostlchronyd[3481]: hz=100 shift_hz=7 freq_scale=1.00000000 nominal_tick=10000 slew_delta_tick=833 max_tick_bias=1000 shift_p11=2 Jun 12 22:22:32 hostlchronyd[34811* Freauencv -19.949 +/- 2.077 ppmreadfrom /var/lib/chrony/drift Jun 12 22:22:32 hostlsystemd[1]: StartedNTPclient/server. [[email protected] -]# systemctl stop chronyd.service [rootOhostl -]# systemctl status chronyd.service chronyd.service - NTPclient/server Loaded: loadedWusr/lib/systemd/system/chronyd.service; enabled) Active: inactive (dead) sinceFri 2015-06-12 22:22:48 PDT; 9s ago Process: 3482 ExecStartPost=/usr/libexec/chrony-helperadd-dhclient-servers (code=exited, status=0/SUCCESS) Process: 3479 ExecStart=/usr/sbin/chronyd -u chrony $OPTIONS (code=exited, status=0/SUCCESS) MainPID: 3481 (code=exited, status=0/SUCCESS) Jun 12 22:22:32 hostlsystemd[1]: StartingNTPclient/server... Jun 12 22:22:32 hostlchronyd[3481]: chronydversion 1.29.1 starting Jun 12 22:22:32 hostlchronyd[3481]: Linuxkernelmajor=3 minor=10 patch=0 Jun 12 22:22:32 hostlchronyd[3481]: hz=100 shift_hz=7 freq_scale=1.00000000 nominal_tick=10000 slew_delta_tick=833 max_tick_bias=1000 shift_p11=2 Jun 12 22:22:32 hostlchronyd[3481]: Frequency -19.949 +/- 2.077 ppmreadfrom /var/lib/chrony/drift Jun 12 22:22:32 hostlsystemd[1]: StartedNTPclient/server. Jun 12 22:22:40 hostlchronyd[3481]: Selectedsource 103.252.195.20 Jun 12 22:22:48 hostlsystemd[1]: StoppingNIPcltmnt/server... Jun 12 22:22:48 hostlsystemd[1]: StoppedNTPclient/server.

In the aboveoutputyou can also see that, it is system process that is starting NTP client.

4> Changing the target mode(previously runlevels)

Until RHEL 6,it was done in “/etc/inittab”, however with RHEL 7 this has changed, andnow.

1. systemctl get-default. [[email protected] -]#systemctl get-default graphical.target

2. systemctl set-default multi-user.target

[[email protected] -]#systemctl set-default multi-user.target rmVetc/systemd/system/default.target' ln -s '/usr/lib/systemd/system/multi-user.target' '/etc/systemd/system/default.target' [[email protected] -]#

Note: We don’t need to remember the complete service name, TAB key works here after

systelctlset-default 5> XFS File system:

In RHEL7 xfs becomes the default filesystem. xfswill support file systems of up to 500TB in size.This is one of most important new features in RHEL 7.

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