Welcome To The Ubuntu Server Guide

The dpkg reconfigure mdadm process will change the /etc/initramfs tools/conf.d/mdadm configuration file. The file has the advantage of being able to pre-configure the system’s behavior, and can alsobe manually edited:BOOT DEGRADED t r u eNoteThe configuration file can be overridden by using a Kernel argument. Using a Kernel argument will allow the system to boot to a degraded array as well:– When the server is booting press Shift to open the Grub menu.– Press e to edit your kernel command options.– Press the down arrow to highlight the kernel line.– Add “bootdegraded true” (without the quotes) to the end of the line.– Press Ctrl x to boot the system.Once the system has booted you can either repair the array see the next section for details, or copy importantdata to another machine due to major hardware failure.RAID MaintenanceThe mdadm utility can be used to view the status of an array, add disks to an array, remove disks, etc: To view the status of an array, from a terminal prompt enter:sudo mdadm D / dev /md0The -D tells mdadm to display detailed information about the /dev/md0 device. Replace /dev/md0with the appropriate RAID device. To view the status of a disk in an array:sudo mdadm E / dev / sda1The output if very similar to the mdadm D command, adjust /dev/sda1 for each disk. If a disk fails and needs to be removed from an array enter:sudo mdadm remove / dev /md0 / dev / sda1Change /dev/md0 and /dev/sda1 to the appropriate RAID device and disk. Similarly, to add a new disk:sudo mdadm add / dev /md0 / dev / sda1Sometimes a disk can change to a faulty state even though there is nothing physically wrong with the drive.It is usually worthwhile to remove the drive from the array then re-add it. This will cause the drive tore-sync with the array. If the drive will not sync with the array, it is a good indication of hardware failure.The /proc/mdstat file also contains useful information about the system’s RAID devices:c a t / p r o c / mdstatP e r s o n a l i t i e s : [ l i n e a r ] [ multipath ] [ raid0 ] [ raid1 ] [ raid6 ] [ raid5 ] [ raid4 ] [raid10 ]md0 : a c t i v e r a i d 1 sda1 [ 0 ] sdb1 [ 1 ]10016384 b l o c k s [ 2 / 2 ] [UU]5

unused d e v i c e s : none The following command is great for watching the status of a syncing drive:watch n1 c a t / p r o c / mdstatPress Ctrl c to stop the watch command.If you do need to replace a faulty drive, after the drive has been replaced and synced, grub will need to beinstalled. To install grub on the new drive, enter the following:sudo grub i n s t a l l / dev /md0Replace /dev/md0 with the appropriate array device name.ResourcesThe topic of RAID arrays is a complex one due to the plethora of ways RAID can be configured. Please seethe following links for more information: Ubuntu Wiki Articles on RAID. Software RAID HOWTO Managing RAID on LinuxLogical Volume Manager (LVM)Logical Volume Manger, or LVM, allows administrators to create logical volumes out of one or multiplephysical hard disks. LVM volumes can be created on both software RAID partitions and standard partitionsresiding on a single disk. Volumes can also be extended, giving greater flexibility to systems as requirementschange.OverviewA side effect of LVM’s power and flexibility is a greater degree of complication. Before diving into the LVMinstallation process, it is best to get familiar with some terms. Physical Volume (PV): physical hard disk, disk partition or software RAID partition formatted asLVM PV. Volume Group (VG): is made from one or more physical volumes. A VG can can be extended byadding more PVs. A VG is like a virtual disk drive, from which one or more logical volumes are carved. Logical Volume (LV): is similar to a partition in a non-LVM system. A LV is formatted with the desiredfile system (EXT3, XFS, JFS, etc), it is then available for mounting and data storage.InstallationAs an example this section covers installing Ubuntu Server Edition with /srv mounted on a LVM volume.During the initial install only one Physical Volume (PV) will be part of the Volume Group (VG). AnotherPV will be added after install to demonstrate how a VG can be extended.There are several installation options for LVM in Guided storage configuration step:6

Select “Use an entire disk”, “Set up this disk as an LVM group”, and Done. This option will create a/boot partition in the local disk and the rest of the disk space is allocated to the LVM group. Select “Use an entire disk”, “Set up this disk as an LVM group”, “Encrypt the LVM group with LUKS”,insert the password (and confirm it), and Done. The output is the same as described above but theLVM group is encrypted. Select “Custom storage layout”, and Done. At this time the only way to configure a system with bothLVM and standard partitions, during installation, is to use this approach. This is the option used inthis example.Follow the installation steps until you get to the Storage configuration step, then:Let’s first create a /boot partition in a local disk. Select the hard disk under AVAILABLE DEVICES, andAdd GPT Parition. Add the size and format (ext4), then select /boot as mount point. Finally, select Create.The /boot partition will be listed under FILE SYSTEM SUMMARY.Next, create standard swap, and / partitions with whichever filesystem you prefer following the steps above.Now the LVM volume group will be created. Select “Create volume group (LVM)”. Enter a name for thevolume group (default is vg0), select the device (LVM physical volume) and the size, and choose “Create”.There is an option to encrypt your volume, if you want it encrypted select “Create encrypted volume” andenter a password (also confirm it). The brand new LVM group (if the default was not changed it is vg0) willbe listed as a device in AVAILABLE DEVICES.To create a LVM logical volume select the created LVM volume group and “Create Logical Volume”. Give ita name (default is lv-0), let’s call it lv-srv since this will be used to mount /srv. Insert the size of the volume,your preferred filesytem format, and select /srv as mount point. Choose “Create”. The LVM logical volumemounted at /srv will be listed in the FILESYSTEM SUMMARY.Finally, select “Done”. Then confirm the changes and continue with the rest of the installation.There are some useful utilities to view information about LVM: pvdisplay: shows information about Physical Volumes. vgdisplay: shows information about Volume Groups. lvdisplay: shows information about Logical Volumes.Extending Volume GroupsContinuing with srv as an LVM volume example, this section covers adding a second hard disk, creating aPhysical Volume (PV), adding it to the volume group (VG), extending the logical volume srv and finallyextending the filesystem. This example assumes a second hard disk has been added to the system. In thisexample, this hard disk will be named /dev/sdb and we will use the entire disk as a physical volume (youcould choose to create partitions and use them as different physical volumes)WarningMake sure you don’t already have an existing /dev/sdb before issuing the commands below. Youcould lose some data if you issue those commands on a non-empty disk.First, create the physical volume, in a terminal execute:sudo p v c r e a t e / dev / sdbNow extend the Volume Group (VG):sudo vgextend vg0 / dev / sdb7

Use vgdisplay to find out the free physical extents - Free PE / size (the size you can allocate). We willassume a free size of 511 PE (equivalent to 2GB with a PE size of 4MB) and we will use the whole free spaceavailable. Use your own PE and/or free space.The Logical Volume (LV) can now be extended by different methods, we will only see how to use the PE toextend the LV:sudo l v e x t e n d / dev / vg0 / s r v l 511The -l option allows the LV to be extended using PE. The -L option allows the LV to be extended usingMeg, Gig, Tera, etc bytes.Even though you are supposed to be able to expand an ext3 or ext4 filesystem without unmounting it first,it may be a good practice to unmount it anyway and check the filesystem, so that you don’t mess up theday you want to reduce a logical volume (in that case unmounting first is compulsory).The following commands are for an EXT3 or EXT4 filesystem. If you are using another filesystem theremay be other utilities available.sudo umount / s r vsudo e 2 f s c k f / dev / vg0 / s r vThe -f option of e2fsck forces checking even if the system seems clean.Finally, resize the filesystem:sudo r e s i z e 2 f s / dev / vg0 / s r vNow mount the partition and check its size.mount / dev / vg0 / s r v / s r v && d f h / s r vResources See the Ubuntu Wiki LVM Articles. See the LVM HOWTO for more information. For more information on fdisk see the fdisk man page.iSCSIThe iSCSI protocol can be used to install Ubuntu on systems with or without hard disks attached, and iBFTcan be used to automate iSCSI setup on installation and boot.Installation on a diskless systemThe first steps of a diskless iSCSI installation are identical to the Installation using debian-installer sectionup to “Hard drive layout”.The installer will display a warning with the following message:No d i s k d r i v e was d e t e c t e d . I f you know t h e name o f t h e d r i v e r needed by yourd i s k d r i v e , you can s e l e c t i t from t h e l i s t .8

Select the item in the list titled login to iSCSI targets.You will be prompted to enter an IP address to scan for iSCSI targets with a description of the format forthe address. Enter the IP address for the location of your iSCSI target and navigate to continue then hitENTERIf authentication is required in order to access the iSCSI device, provide the username in the next field.Otherwise, leave it blank.If your system is able to connect to the iSCSI provider, you should see a list of available iSCSI targets wherethe operating system can be installed. The list should be similar to the following :S e l e c t t h e iSCSI t a r g e t s you wish t o u s e .iSCSI t a r g e t s on 1 9 2 . 1 6 8 . 1 . 2 9 : 3 2 6 0 :[ ] i q n .2016 03. TrustyS i s c s i t a r g e t : s t o r a g e . s y s 0 Go Back Continue Select the iSCSI target that you want to use with the space bar. Use the arrow keys to navigate to the targetthat you want to select.Navigate to Continue and hit ENTER.If the connection to the iSCSI target is successful, you will be prompted with the [!!] Partition disksinstallation menu. The rest of the procedure is identical to any normal installation on attached disks. Oncethe installation is completed, you will be asked to reboot.Installation on a system with disk attachedAgain, the iSCSI installation on a normal server with one or many disks attached is identical to the Installation using debian-installer section until we reach the disk partitioning menu. Instead of using any of theGuided selection, we need to perform the following steps :Navigate to the Manual menu entrySelect the Configure iSCSI Volumes menu entryChoose the Log into iSCSI targetsYou will be prompted to Enter an IP address to scan for iSCSI targets. with a description of the format forthe address. Enter the IP address and navigate to continue then hit ENTERIf authentication is required in order to access the iSCSI device, provide the username in the next field orleave it blank.If your system is able to connect to the iSCSI provider, you should see a list of available iSCSI targets wherethe operating system can be installed. The list should be similar to the following :S e l e c t t h e iSCSI t a r g e t s you wish t o u s e .iSCSI t a r g e t s on 1 9 2 . 1 6 8 . 1 . 2 9 : 3 2 6 0 :[ ] i q n .2016 03. TrustyS i s c s i t a r g e t : s t o r a g e . s y s 0 Go Back Continue Select the iSCSI target that you want to use with the space bar. Use the arrow keys to navigate to the targetthat you want to select9

Navigate to Continue and hit ENTER.If successful, you will come back to the menu asking you to Log into iSCSI targets. Navigate to Finish andhit ENTERThe newly connected iSCSI disk will appear in the overview section as a device prefixed with SCSI. Thisis the disk that you should select as your installation disk. Once identified, you can choose any of thepartitioning methods.WarningDepending on your system configuration, there may be other SCSI disks attached to the system.Be very careful to identify the proper device before proceeding with the installation. Otherwise,irreversible data loss may result from performing an installation on the wrong disk.Installation with iBFTIn order to setup iSCSI based on the iBFT (iSCSI Boot Firmware Table) on the installation and boot,append these options at the installer prompt (or to the preseed file):d i s k d e t e c t / i b f t / e n a b l e t r u e partman i s c s i / i s c s i a u t o t r u eThis should probe for iBFT information and configure network interface(s) and iSCSI target(s) accordinglyduring the installation, and configure system boot (initramfs) to do that too in order to find the root device.Warning The support for iBFT is available in the debian-installer on netboot images as of2019-06-20 and (expected) on ISO images for the 18.04.3 point release and later.Rebooting to an iSCSI targetThe procedure is specific to your hardware platform. As an example, here is how to reboot to your iSCSItarget using iPXEiPXE dhcpC o n f i g u r i n g ( n e t 0 5 2 : 5 4 : 0 0 : a4 : f 2 : a9 ) . . . . . . . okiPXE s a n b oo t i s c s i : 1 9 2 . 1 6 8 . 1 . 2 9 : : : : i q n .2016 03. TrustyS i s c s i t a r g e t : s t o r a g e .sys0If the procedure is successful, you should see the Grub menu appear on the screen.Package ManagementUbuntu features a comprehensive package management system for installing, upgrading, configuring, andremoving software. In addition to providing access to an organized base of over 60,000 software packages foryour Ubuntu computer, the package management facilities also feature dependency resolution capabilitiesand software update checking.Several tools are available for interacting with Ubuntu’s package management system, from simple commandline utilities which may be easily automated by system administrators, to a graphical interface which is easyto use by those new to Ubuntu.10

IntroductionUbuntu’s package management system is derived from the same system used by the Debian GNU/Linuxdistribution. The package files contain all of the necessary files, meta-data, and instructions to implement aparticular functionality or software application on your Ubuntu computer.Debian package files typically have the extension .deb, and usually exist in repositories which are collectionsof packages found online or on physical media, such as CD-ROM discs. Packages are normally in a precompiled binary format; thus installation is quick and requires no compiling of software.Many packages use dependencies. Dependencies are additional packages required by the principal packagein order to function properly. For example, the speech synthesis package festival depends upon the packagealsa utils, which is a package supplying the ALSA sound library tools needed for audio playback. In orderfor festival to function, it and all of its dependencies must be installed. The software management tools inUbuntu will do this automatically.AptThe apt command is a powerful command-line tool, which works with Ubuntu’s Advanced Packaging Tool(APT) performing such functions as installation of new software packages, upgrade of existing softwarepackages, updating of the package list index, and even upgrading the entire Ubuntu system.Some examples of popular uses for the apt utility: Install a Package: Installation of packages using the apt tool is quite simple. For example, to installthe nmap network scanner, type the following:sudo apt i n s t a l l nmap Remove a Package: Removal of a package (or packages) is also straightforward. To remove thepackage installed in the previous example, type the following:sudo apt remove nmapTipMultiple Packages: You may specify multiple packages to be installed or removed, separated by spaces.NoticeScripting: While apt is a command-line tool, it is intended to be used interactively, and notto be called from non-interactive scripts. The apt get command should be used in scripts(perhaps with the quiet flag). For basic commands the syntax of the two tools is identical.Also, adding the purge option to apt remove will remove the package configuration files as well.This may or may not be the desired effect, so use with caution. Update the Package Index: The APT package index is essentially a database of available packagesfrom the repositories defined in the /etc/apt/sources. list file and in the /etc/apt/sources. list .d directory. To update the local package index with the latest changes made in the repositories, type thefollowing:sudo apt update Upgrade Packages: Over time, updated versions of packages currently installed on your computermay become available from the package repositories (for example security updates). To upgrade yoursystem, first, update your package index as outlined above, and then type:sudo apt upgrade11

For information on upgrading to a new Ubuntu release see Upgrading.Actions of the apt command, such as installation and removal of packages, are logged in the /var/log/dpkg.loglog file.For further information about the use of APT, read the comprehensive APT User’s Guide or type:apt h e l pAptitudeLaunching Aptitude with no command-line options will give you a menu-driven, text-based front-end tothe Advanced Packaging Tool (APT) system. Many of the common package management functions, suchas installation, removal, and upgrade, can be performed in Aptitude with single-key commands, which aretypically lowercase letters.Aptitude is best suited for use in a non-graphical terminal environment to ensure proper functioning ofthe command keys. You may start the menu-driven interface of Aptitude as a normal user by typing thefollowing command at a terminal prompt:sudo a p t i t u d eWhen Aptitude starts, you will see a menu bar at the top of the screen and two panes below the menu bar.The top pane contains package categories, such as New Packages and Not Installed Packages. The bottompane contains information related to the packages and package categories.Using Aptitude for package management is relatively straightforward, and the user interface makes commontasks simple to perform. The following are examples of common package management functions as performedin Aptitude: Install Packages: To install a package, locate the package via the Not Installed Packages packagecategory, by using the keyboard arrow keys and the ENTER key. Highlight the desired package,then press the key. The package entry should turn green, indicating that it has been marked forinstallation. Now press g to be presented with a summary of package actions. Press g again, anddownloading and installation of the package will commence. When finished, press ENTER, to returnto the menu. Remove Packages: To remove a package, locate the package via the Installed Packages packagecategory, by using the keyboard arr

Welcome to the Ubuntu Server Guide! Changes, Errors, and Bugs This is the current edition for Ubuntu 20.04 LTS, Focal Fossa. Ubuntu serverguides for previous LTS versions: . Ubuntu’s package management system is derived from the same syst