In ubuntu 15.04 systemd is introduced as previously the OS starts with init (ubuntu's custom start up where it loads all boot up modules to start the system services).
systemd's model for starting processes (units) is "lazy dependency-based", i. e. a unit will only start if and when some other starting unit depends on it. During boot, systemd starts a "root unit" (default.target, can be overridden in grub), which then transitively expands and starts its dependencies. A new unit needs to add itself as a dependency of a unit of the boot sequence (commonly multi-user.target) in order to become active. systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. systemd provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, supports snapshotting and restoring of the system state, maintains mount and auto mount points and implements an elaborate transactional dependency-based service control logic.
Linux kernel 3.19 gives more push with operating system in gaining its performance of network,file systems behaviour
New features in 15.04
Updated Packages
systemd's model for starting processes (units) is "lazy dependency-based", i. e. a unit will only start if and when some other starting unit depends on it. During boot, systemd starts a "root unit" (default.target, can be overridden in grub), which then transitively expands and starts its dependencies. A new unit needs to add itself as a dependency of a unit of the boot sequence (commonly multi-user.target) in order to become active. systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. systemd provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, supports snapshotting and restoring of the system state, maintains mount and auto mount points and implements an elaborate transactional dependency-based service control logic.
Linux kernel 3.19 gives more push with operating system in gaining its performance of network,file systems behaviour
Download Ubuntu 15.04
Images can be downloaded from a location near you.
You can download ISOs from:
http://releases.ubuntu.com/15.04/ (Ubuntu Desktop, Server, and Snappy Core)
http://cloud-images.ubuntu.com/releases/15.04/release/ (Ubuntu Cloud Server)
http://cdimage.ubuntu.com/netboot/15.04/ (Ubuntu Netboot)
http://cloud-images.ubuntu.com/releases/15.04/release/ (Ubuntu Cloud Server)
http://cdimage.ubuntu.com/netboot/15.04/ (Ubuntu Netboot)
http://cdimage.ubuntu.com/kubuntu/releases/15.04/release/ (Kubuntu)
http://cdimage.ubuntu.com/lubuntu/releases/15.04/release/ (Lubuntu)
http://cdimage.ubuntu.com/ubuntustudio/releases/15.04/release/ (Ubuntu Studio)
http://cdimage.ubuntu.com/ubuntu-gnome/releases/15.04/release/ (Ubuntu GNOME)
http://cdimage.ubuntu.com/ubuntukylin/releases/15.04/release/ (Ubuntu Kylin)
http://cdimage.ubuntu.com/ubuntu-mate/releases/15.04/release/ (Ubuntu MATE)
http://cdimage.ubuntu.com/xubuntu/releases/15.04/release/ (Xubuntu)
http://cdimage.ubuntu.com/lubuntu/releases/15.04/release/ (Lubuntu)
http://cdimage.ubuntu.com/ubuntustudio/releases/15.04/release/ (Ubuntu Studio)
http://cdimage.ubuntu.com/ubuntu-gnome/releases/15.04/release/ (Ubuntu GNOME)
http://cdimage.ubuntu.com/ubuntukylin/releases/15.04/release/ (Ubuntu Kylin)
http://cdimage.ubuntu.com/ubuntu-mate/releases/15.04/release/ (Ubuntu MATE)
http://cdimage.ubuntu.com/xubuntu/releases/15.04/release/ (Xubuntu)
Updated Packages
As with every new release, packages--applications and software of all kinds--are being updated at a rapid pace. Many of these packages came from an automatic sync from Debian's unstable branch; others have been explicitly pulled in for Ubuntu 15.04.
For a list of all packages being accepted for Ubuntu 15.04, please subscribe to vivid-changes.
Linux kernel 3.19
For servers we see a number of performance related improvements including network send batching and the introduction of the data centre congestion algorithm, as well as the introduction of discard support in Device Mapper raid configurations. There are also improvements to inode locking which should show benefits under heavy load. Netfilter (nftables) continues to evolve gaining facilities for package logging and dumping. A number of filesystems gained minor new features, including btrfs which improved its disk replacement in raid 5 and 6 configurations, and support for scrubbing in those. NFS gained hole punching and preallocation support. Overlayfs finally moved upstream so simplifying its provision in Ubuntu. On the networking side we see the start of routing and switch offload support, and the addition of checksum offload for Generic UDP Encapsulation. Finally we see the introduction of the cutely named foo-over-UDP support, allowing a number of other protocols to nest inside.
On cloud we saw a number of Device Mapper thin storage improvements including performance improvements under high load, and speedier discards in these thin configurations. Xen saw a number of minor fixes. For Hyper-v we see the ext2 filesystem gain freeze support allowing default configurations to be snapshotted. Openvswitch continued to evolve gaining basic MPLS support and Geneve tunnelling.
Boot and service management
systemd has replaced Upstart as the standard boot and service manager on all Ubuntu flavors except Touch. At the time of the 15.04 release there are no known major problems which prevent booting. The only service which does not currently start is Juju, which will be fixed in a post-release update soon; all other packaged Ubuntu services are expected to work.
Upstart continues to control user sessions.
If your system does not boot after installing or upgrading, please file a bug report and tag it with `systemd-boot`. Please see/usr/share/doc/systemd/README.Debian about how to debug early boot or shutdown problems.
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