DOCSLIB.ORG

Welcome to the Ubuntu Server Guide ! Basic Installation Preparing to Install

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Welcome to the Ubuntu Server Guide ! Basic Installation Preparing to Install 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: 18.04 (PDF), 16.04 (PDF). If you find any errors or have suggestions for improvements to pages, please use the link at thebottomof each topic titled: “Help improve this document in the forum.” This link will take you to the Server Discourse forum for the specific page you are viewing. There you can share your comments or let us know aboutbugs with each page. Offline Download this guide as a PDF Support There are a couple of different ways that Ubuntu Server Edition is supported: commercial support and community support. The main commercial support (and development funding) is available from Canonical, Ltd. They supply reasonably- priced support contracts on a per desktop or per server basis. For more information see the Ubuntu Advantage page. Community support is also provided by dedicated individuals and companies that wish to make Ubuntu the best distribution possible. Support is provided through multiple mailing lists, IRC channels, forums, blogs, wikis, etc. The large amount of information available can be overwhelming, but a good search engine query can usually provide an answer to your questions. See the Ubuntu Support page for more information. Basic installation This chapter provides an overview of installing Ubuntu 20.04 Server Edition. There is more detailed docu- mentation on other installer topics. Preparing to Install This section explains various aspects to consider before starting the installation. System requirements Ubuntu 20.04 Server Edition provides a common, minimalist base for a variety of server applications, such as file/print services, web hosting, email hosting, etc. This version supports four 64-bit architectures: • amd64 (Intel/AMD 64-bit) • arm64 (64-bit ARM) • ppc64el (POWER8 and POWER9) • s390x (IBM Z and LinuxONE) The recommended system requirements are: • CPU: 1 gigahertz or better 1 • RAM: 1 gigabyte or more • Disk: a minimum of 2.5 gigabytes Server and Desktop Differences The Ubuntu Server Edition and the Ubuntu Desktop Edition use the same apt repositories, making it just as easy to install a server application on the Desktop Edition as on the Server Edition. One major difference is that the graphical environment used for the Desktop Edition is not installed for the Server. This includes the graphics server itself, the graphical utilities and applications, and the various user-supporting services needed by desktop users. Backing Up Before installing Ubuntu Server Edition you should make sure all data on the system is backed up. If this is not the first time an operating system has been installed on your computer, it is likely you willneed to re-partition your disk to make room for Ubuntu. Any time you partition your disk, you should be prepared to lose everything on the disk should you make a mistake or something goes wrong during partitioning. The programs used in installation are quite reliable, most have seen years of use, but they also perform destructive actions. Preparing install media There are platform specific step-by-step examples for s390x LPAR, z/VM and ppc64el installations. For amd64, download the install image from https://releases.ubuntu.com/20.04/. There are many ways to boot the installer but the simplest and commonest way is to create a bootable USB stick to boot the system to be installed with (tutorials for other operating systems are also available). Booting the installer Plug the USB stick into the system to be installed and start it. Most computers will automatically boot from USB or DVD, though in some cases this is disabled to improve boot times. If you don’t see the boot message and the “Welcome” screen which should appear after it, you will need to set your computer to boot from the install media. There should be an on-screen message when the computer starts telling you what key to press for settings or a boot menu. Depending on the manufacturer, this could be Escape, F2,F10 or F12. Simply restart your computer and hold down this key until the boot menu appears, then select the drive with the Ubuntu install media. If you are still having problems, check out the Ubuntu Community documentation on booting from CD/DVD. After a few moments, the installer will start in its language selection screen. welcome_c|690x517 2 Using the installer The installer is designed to be easy to use and have sensible defaults so for a first install you can mostly just accept the defaults for the most straightforward install: • Choose your language • Update the installer (if offered) • Select your keyboard layout • Do not configure networking (the installer attempts to configure wired network interfaces viaDHCP, but you can continue without networking if this fails) • Do not configure a proxy or custom mirror unless you have to in your network • For storage, leave “use an entire disk” checked, and choose a disk to install to, then select “Done” on the configuration screen and confirm the install • Enter a username, hostname and password • Just select Done on the SSH and snap screens • You will now see log messages as the install is completed • Select restart when this is complete, and log in using the username and password provided There is more detailed documentation on all these options. Advanced Installation Software RAID Redundant Array of Independent Disks “RAID” is a method of using multiple disks to provide different balances of increasing data reliability and/or increasing input/output performance, depending on the RAID level being used. RAID is implemented in either software (where the operating system knows about both drives and actively maintains both of them) or hardware (where a special controller makes the OS think there’s only one drive and maintains the drives ‘invisibly’). The RAID software included with current versions of Linux (and Ubuntu) is based on the ‘mdadm’ driver and works very well, better even than many so-called ‘hardware’ RAID controllers. This section will guide you through installing Ubuntu Server Edition using two RAID1 partitions on two physical hard drives, one for / and another for swap. RAID Configuration Follow the installation steps until you get to the Guided storage configuration step, then: Select Custom storage layout. Create the /boot partition in a local disk. So select one of the devices listed in available devices and Add GPT Partition. Next, enter the partition size, then choose the desired Format (ext4) and /boot as mount point. And finally, select Create. Now to create the RAID device select Create software RAID (md) under AVAILABLE DEVICES. Add the name of the RAID disk (the default is md0). For this example, select “1 (mirrored)” in RAID level, but if you are using a different setup choose the appropriate type (RAID0 RAID1 RAID5 RAID6 RAID10). Note In order to use RAID5, RAID6 and RAID10 you need more than two drives. Using RAID0 or RAID1 only two drives are required. 3 Select the devices that will be used by this RAID device. The real devices can be marked as active or spare, by default it becomes active when is selected. Select the Size of the RAID device. Select Create. The new RAID device (md0 if you did not change the default) will show up in the available devices list, with software RAID 1 type and the chosen size. Repeat steps above for the other RAID devices. Partitioning Select the RAID 1 device created (md0) then select “Add GPT Partition”. Next, select the Size of the partition. This partition will be the swap partition, and a general rule for swap size is twice that of RAM. Enter the partition size, then choose swap in Format. And finally, select Create. Note A swap partition size of twice the available RAM capacity may not always be desirable, especially on systems with large amounts of RAM. Calculating the swap partition size for servers is highly dependent on how the system is going to be used. For the / partition once again select the RAID 1 device then “Add GPT Partition”. Use the rest of the free space on the device, choose the format (default is ext4) and select / as mount point, then Create. Repeat steps above for the other partitions. Once it is finished select “Done”. The installation process will then continue normally. Degraded RAID At some point in the life of the computer a disk failure event may occur. When this happens, using Software RAID, the operating system will place the array into what is known as a degraded state. If the array has become degraded, due to the chance of data corruption, by default Ubuntu Server Edition will boot to initramfs after thirty seconds. Once the initramfs has booted there is a fifteen second prompt giving you the option to go ahead and boot the system, or attempt manual recover. Booting to the initramfs prompt may or may not be the desired behavior, especially if the machine is in a remote location. Booting to a degraded array can be configured several ways: • The dpkg-reconfigure utility can be used to configure the default behavior, and during the processyou will be queried about additional settings related to the array. Such as monitoring, email alerts, etc. To reconfigure mdadm enter the following: sudo dpkg−reconfigure mdadm • The dpkg−reconfigure mdadm process will change the /etc/initramfs−tools/conf.d/mdadm configura- tion file. The file has the advantage of being able to pre-configure the system’s behavior, andcanalso be manually edited: BOOT_DEGRADED=true 4 Note The configuration file can be overridden by using a Kernel argument.
Load more

Recommended publications
  • Fully Eliminated the Language Barrier and Enable Ease of Communication Through This Application
    IOSR Journal of Computer Engineering (IOSR-JCE) e-ISSN: 2278-0661, p- ISSN: 2278-8727Volume 16, Issue 2, Ver. XI (Mar-Apr. 2014), PP 113-119 www.iosrjournals.org Alltalk™- A Windows Phone Messenger with Cross Language Communication Shruti Shetye1, Akhil Abraham2, Royston Pinto3, Sonali Vaidya4 1(BE-IT Student, Information Technology, St. FrancisInstitute of Technology, India) 2(BE-IT Student, Information Technology, St. Francis Institute of Technology, India) 3(BE-IT Student, Information Technology, St. Francis Institute of Technology, India 4(Lecturer, Information Technology, St. Francis Institute of Technology, India) __________________________________________________________________________________ Abstract:In day to day life, messengers or chatting applications provide facility for instant messaging over the internet. Exchange of messages takes place in universally used languages like English, French, etc. where both the users know how to communicate in a common language. Thus chatting on mobile phones is a luxury when both the parties involved know a common language. Hence we have implemented ALLTALK™ which is a Windows 8 phone based chatting application which makes cross language communication possible using mobile programming and networking technology.This application will enable the communication between two persons irrespective of the language each user wishes to use individually. The various modes of communication available in this messenger are through text and voice. Due to the best processing power provided among the available smartphones and high battery life we choose to work on windows 8 platform. Thus we have successfully eliminated the language barrier and enable ease of communication through this application. Keywords: Cross Language communication, instant messenger, socket connection, translator,Windows phone app.
    [Show full text]
  • Campus Networking Best Practices Session 5: Wireless
    Campus Networking Best Practices Session 5: Wireless LAN Hervey Allen Dale Smith NSRC & University of Oregon University of Oregon & NSRC [email protected] [email protected] Wireless LAN • Provide wireless network across your campus that has the following characteristics: – Authentication – only allow your users – Roaming – allow users to start up in one section of your network, then move to another location – Runs on your campus network Firewall/ Border Traffic Shaper Router Wireless REN switch Authentication Core Gateway Router Core Servers Network Access Control (NAC) Enterprise Identity Management • Processes and Documentation of users. – Now you must deal with this. – What to use as the back-end user store? • LDAP • Active Directory • Kerberos • Other? – Will this play nice with future use? • email, student/staff information, resource access, ... Identity Management Cont. • An example of such a project can be seen here: – http://ccadmin.uoregon.edu/idm/ • This is a retrofit on to an already retrofitted system. • Learn from others and try to avoid this situation if possible. A Wireless Captive Portal The Wireless Captive Portal • Previous example was very simple. • A Captive Portal is your chance to: – Explain your Acceptable Use Policies – Decide if you must authenticate, or – Allow users on your network and monitor for problems instead (alternate solution). – Anything else? Branding? What's Happening? • remember our initial network diagrams...? • Do you think our hotel built their own solution? • Probably not... Commercial Solutions • Aruba http://www.arubanetworks.com/ • Bradford Networks – http://www.bradfordnetworks.com/ • Cisco NAC Appliance (Clean Access) – http://www.cisco.com/en/US/products/ps6128/ • Cisco Wireless LAN Controllers – http://www.cisco.com/en/US/products/hw/wireless/ • Enterasys http://www.enterasys.com/ • Vernier http://www.verniernetworks.com Open Source Solutions • CoovaChilli (morphed from Chillispot) – http://coova.org/wiki/index.php/CoovaChilli – Uses RADIUS for access and accounting.
    [Show full text]
  • Chapter 3. Booting Operating Systems
    Chapter 3. Booting Operating Systems Abstract: Chapter 3 provides a complete coverage on operating systems booting. It explains the booting principle and the booting sequence of various kinds of bootable devices. These include booting from floppy disk, hard disk, CDROM and USB drives. Instead of writing a customized booter to boot up only MTX, it shows how to develop booter programs to boot up real operating systems, such as Linux, from a variety of bootable devices. In particular, it shows how to boot up generic Linux bzImage kernels with initial ramdisk support. It is shown that the hard disk and CDROM booters developed in this book are comparable to GRUB and isolinux in performance. In addition, it demonstrates the booter programs by sample systems. 3.1. Booting Booting, which is short for bootstrap, refers to the process of loading an operating system image into computer memory and starting up the operating system. As such, it is the first step to run an operating system. Despite its importance and widespread interests among computer users, the subject of booting is rarely discussed in operating system books. Information on booting are usually scattered and, in most cases, incomplete. A systematic treatment of the booting process has been lacking. The purpose of this chapter is to try to fill this void. In this chapter, we shall discuss the booting principle and show how to write booter programs to boot up real operating systems. As one might expect, the booting process is highly machine dependent. To be more specific, we shall only consider the booting process of Intel x86 based PCs.
    [Show full text]
  • How to Create a Custom Live CD for Secure Remote Incident Handling in the Enterprise
    How to Create a Custom Live CD for Secure Remote Incident Handling in the Enterprise Abstract This paper will document a process to create a custom Live CD for secure remote incident handling on Windows and Linux systems. The process will include how to configure SSH for remote access to the Live CD even when running behind a NAT device. The combination of customization and secure remote access will make this process valuable to incident handlers working in enterprise environments with limited remote IT support. Bert Hayes, [email protected] How to Create a Custom Live CD for Remote Incident Handling 2 Table of Contents Abstract ...........................................................................................................................................1 1. Introduction ............................................................................................................................5 2. Making Your Own Customized Debian GNU/Linux Based System........................................7 2.1. The Development Environment ......................................................................................7 2.2. Making Your Dream Incident Handling System...............................................................9 2.3. Hardening the Base Install.............................................................................................11 2.3.1. Managing Root Access with Sudo..........................................................................11 2.4. Randomizing the Handler Password at Boot Time ........................................................12
    [Show full text]
  • TLS in the Wild: an Internet-Wide Analysis of TLS-Based Protocols for Electronic Communication
    TLS in the wild: An Internet-wide analysis of TLS-based protocols for electronic communication Ralph Holz∗, Johanna Amannz, Olivier Mehaniy, Matthias Wachsx, Mohamed Ali Kaafary ∗University of Sydney, Australia, Email: [email protected] yData61/CSIRO, Sydney, Australia, Email: [email protected] zICSI, Berkeley, USA, Email: [email protected] xTechnical University of Munich, Germany, Email: [email protected] This is a preprint of the camera-ready version to appear at NDSS 2016. Last update: 19 Dec 2015. Abstract—Email and chat still constitute the majority of in 2018 [11]. As for chat, the most widely used standard- electronic communication on the Internet. The standardisation based networks are IRC group chats and the XMPP instant and acceptance of protocols such as SMTP, IMAP, POP3, XMPP, messaging and multi-user conferencing network. and IRC has allowed to deploy servers for email and chat in a decentralised and interoperable fashion. These protocols can be In their early days, email protocols such as SMTP, POP3, secured by providing encryption with TLS—directly or via the and IMAP were designed with no special focus on security. STARTTLS extension. X.509 PKIs and ad hoc methods can be In particular, authentication in SMTP was introduced a while leveraged to authenticate communication peers. However, secure after the protocol’s standardisation, initially as a way to configuration is not straight-forward and many combinations fight spam. User agents started to move towards encryption of encryption and authentication mechanisms lead to insecure deployments and potentially compromise of data in transit. In and authenticated connections gradually, using the then-new this paper, we present the largest study to date that investigates SSL 3 and later the TLS protocols to protect the transport the security of our email and chat infrastructures.
    [Show full text]
  • In Search of the Ideal Storage Configuration for Docker Containers
    In Search of the Ideal Storage Configuration for Docker Containers Vasily Tarasov1, Lukas Rupprecht1, Dimitris Skourtis1, Amit Warke1, Dean Hildebrand1 Mohamed Mohamed1, Nagapramod Mandagere1, Wenji Li2, Raju Rangaswami3, Ming Zhao2 1IBM Research—Almaden 2Arizona State University 3Florida International University Abstract—Containers are a widely successful technology today every running container. This would cause a great burden on popularized by Docker. Containers improve system utilization by the I/O subsystem and make container start time unacceptably increasing workload density. Docker containers enable seamless high for many workloads. As a result, copy-on-write (CoW) deployment of workloads across development, test, and produc- tion environments. Docker’s unique approach to data manage- storage and storage snapshots are popularly used and images ment, which involves frequent snapshot creation and removal, are structured in layers. A layer consists of a set of files and presents a new set of exciting challenges for storage systems. At layers with the same content can be shared across images, the same time, storage management for Docker containers has reducing the amount of storage required to run containers. remained largely unexplored with a dizzying array of solution With Docker, one can choose Aufs [6], Overlay2 [7], choices and configuration options. In this paper we unravel the multi-faceted nature of Docker storage and demonstrate its Btrfs [8], or device-mapper (dm) [9] as storage drivers which impact on system and workload performance. As we uncover provide the required snapshotting and CoW capabilities for new properties of the popular Docker storage drivers, this is a images. None of these solutions, however, were designed with sobering reminder that widespread use of new technologies can Docker in mind and their effectiveness for Docker has not been often precede their careful evaluation.
    [Show full text]
  • Iptables with Shorewall!
    Iptables with shorewall! Table of Contents 1. Install swarmlab-sec (Home PC) . 1 2. shorewall . 1 2.1. Installation . 2 3. Basic Two-Interface Firewall. 2 4. Shorewall Concepts . 3 4.1. zones — Shorewall zone declaration file . 3 4.2. interfaces — Shorewall interfaces file. 4 4.3. policy — Shorewall policy file . 4 4.4. rules — Shorewall rules file . 4 4.5. Compile then Execute . 4 5. Three-Interface Firewall. 5 5.1. zones . 6 5.2. interfaces . 6 5.3. policy . 7 5.4. rules . 7 5.5. masq - Shorewall Masquerade/SNAT definition file . 7 5.6. snat — Shorewall SNAT/Masquerade definition file . 8 5.7. Compile and Execute . 8 1. Install swarmlab-sec (Home PC) HowTo: See http://docs.swarmlab.io/lab/sec/sec.adoc.html NOTE Assuming you’re already logged in 2. shorewall Shorewall is an open source firewall tool for Linux that builds upon the Netfilter (iptables/ipchains) system built into the Linux kernel, making it easier to manage more complex configuration schemes by providing a higher level of abstraction for describing rules using text files. More: wikipedia 1 NOTE Our docker instances have only one nic to add more nic’s: create netowrk frist docker network create --driver=bridge --subnet=192.168.0.0/16 net1 docker network create --driver=bridge --subnet=192.168.0.0/16 net2 docker network create --driver=bridge --subnet=192.168.0.0/16 net3 then connect network to container connect network created to container docker network connect net1 master docker network connect net1 worker1 docker network connect net2 master docker network connect net2 worker2 now let’s look at the following image 2.1.
    [Show full text]
  • Linux Boot Loaders Compared
    Linux Boot Loaders Compared L.C. Benschop May 29, 2003 Copyright c 2002, 2003, L.C. Benschop, Eindhoven, The Netherlands. Per- mission is granted to make verbatim copies of this document. This is version 1.1 which has some minor corrections. Contents 1 introduction 2 2 How Boot Loaders Work 3 2.1 What BIOS does for us . 3 2.2 Parts of a boot loader . 6 2.2.1 boot sector program . 6 2.2.2 second stage of boot loader . 7 2.2.3 Boot loader installer . 8 2.3 Loading the operating system . 8 2.3.1 Loading the Linux kernel . 8 2.3.2 Chain loading . 10 2.4 Configuring the boot loader . 10 3 Example Installations 11 3.1 Example root file system and kernel . 11 3.2 Linux Boot Sector . 11 3.3 LILO . 14 3.4 GNU GRUB . 15 3.5 SYSLINUX . 18 3.6 LOADLIN . 19 3.7 Where Can Boot Loaders Live . 21 1 4 RAM Disks 22 4.1 Living without a RAM disk . 22 4.2 RAM disk devices . 23 4.3 Loading a RAM disk at boot time . 24 4.4 The initial RAM disk . 24 5 Making Diskette Images without Diskettes 25 6 Hard Disk Installation 26 7 CD-ROM Installation 29 8 Conclusions 31 1 introduction If you use Linux on a production system, you will only see it a few times a year. If you are a hobbyist who compiles many kernels or who uses many operating systems, you may see it several times per day.
    [Show full text]
  • Engineering at Johns Hopkins University! We Look Forward to Meeting You When You Arrive on Campus for Orientation
    Eng in eering 1 01 2019-2020 p rogr am p lanni ng gui de for fi rst-y ear e ngi neering s tudents Welcome to the Whiting School of Engineering at Johns Hopkins University! We look forward to meeting you when you arrive on campus for orientation. In the meantime, we have prepared the First-Year Academic Guide and Engineering 101 to get you started. The Academic Guide includes information for all first-year students at Hopkins, while Engineering 101 is directed specifically to engineering students. Engineering 101 contains information about all of the majors in the School of Engineering, including recommended first semester class schedules. You’ll also find out about some opportunities to join student groups. We hope that these materials help you learn about the Hopkins community and the options available to you. Again, welcome to Hopkins and we’ll see you in August! Linda Moulton, Denise Shipley, Lashell Silver, Eric Simmons, Janet Weise, and Betty Zee Johns Hopkins University Whiting School of Engineering Office of Academic Affairs—Engineering Advising Wyman Park Building Suite N125 3400 N. Charles Street Baltimore, MD 21218-2681 410-516-7395 [email protected] https://engineering.jhu.edu/advising/ Nondiscrimination Statement The Johns Hopkins University is committed to equal opportunity and providing a safe and non- discriminatory educational and working environment for its students, trainees, faculty, staff, post-doctoral fellows, residents, and other members of the University community. To that end, the university seeks to provide community members with an environment that is free from discrimination and harassment on the basis of sex, gender, marital status, pregnancy, race, color, ethnicity, national origin, age, disability, religion, sexual orientation, gender identity or expression, veteran status or other legally protected characteristic.
    [Show full text]
  • Kdump, a Kexec-Based Kernel Crash Dumping Mechanism
    Kdump, A Kexec-based Kernel Crash Dumping Mechanism Vivek Goyal Eric W. Biederman Hariprasad Nellitheertha IBM Linux NetworkX IBM [email protected] [email protected] [email protected] Abstract important consideration for the success of a so- lution has been the reliability and ease of use. Kdump is a crash dumping solution that pro- Kdump is a kexec based kernel crash dump- vides a very reliable dump generation and cap- ing mechanism, which is being perceived as turing mechanism [01]. It is simple, easy to a reliable crash dumping solution for Linux R . configure and provides a great deal of flexibility This paper begins with brief description of what in terms of dump device selection, dump saving kexec is and what it can do in general case, and mechanism, and plugging-in filtering mecha- then details how kexec has been modified to nism. boot a new kernel even in a system crash event. The idea of kdump has been around for Kexec enables booting into a new kernel while quite some time now, and initial patches for preserving the memory contents in a crash sce- kdump implementation were posted to the nario, and kdump uses this feature to capture Linux kernel mailing list last year [03]. Since the kernel crash dump. Physical memory lay- then, kdump has undergone significant design out and processor state are encoded in ELF core changes to ensure improved reliability, en- format, and these headers are stored in a re- hanced ease of use and cleaner interfaces. This served section of memory. Upon a crash, new paper starts with an overview of the kdump de- kernel boots up from reserved memory and pro- sign and development history.
    [Show full text]
  • Oracle® Linux 7 Managing File Systems
    Oracle® Linux 7 Managing File Systems F32760-07 August 2021 Oracle Legal Notices Copyright © 2020, 2021, Oracle and/or its affiliates. This software and related documentation are provided under a license agreement containing restrictions on use and disclosure and are protected by intellectual property laws. Except as expressly permitted in your license agreement or allowed by law, you may not use, copy, reproduce, translate, broadcast, modify, license, transmit, distribute, exhibit, perform, publish, or display any part, in any form, or by any means. Reverse engineering, disassembly, or decompilation of this software, unless required by law for interoperability, is prohibited. The information contained herein is subject to change without notice and is not warranted to be error-free. If you find any errors, please report them to us in writing. If this is software or related documentation that is delivered to the U.S. Government or anyone licensing it on behalf of the U.S. Government, then the following notice is applicable: U.S. GOVERNMENT END USERS: Oracle programs (including any operating system, integrated software, any programs embedded, installed or activated on delivered hardware, and modifications of such programs) and Oracle computer documentation or other Oracle data delivered to or accessed by U.S. Government end users are "commercial computer software" or "commercial computer software documentation" pursuant to the applicable Federal Acquisition Regulation and agency-specific supplemental regulations. As such, the use, reproduction, duplication, release, display, disclosure, modification, preparation of derivative works, and/or adaptation of i) Oracle programs (including any operating system, integrated software, any programs embedded, installed or activated on delivered hardware, and modifications of such programs), ii) Oracle computer documentation and/or iii) other Oracle data, is subject to the rights and limitations specified in the license contained in the applicable contract.
    [Show full text]
  • Linux Core Dumps
    Linux Core Dumps Kevin Grigorenko [email protected] Many Interactions with Core Dumps systemd-coredump abrtd Process Crashes Ack! 4GB File! Most Interactions with Core Dumps Poof! Process Crashes systemd-coredump Nobody abrtd Looks core kdump not Poof! Kernel configured Crashes So what? ● Crashes are problems! – May be symptoms of security vulnerabilities – May be application bugs ● Data corruption ● Memory leaks – A hard crash kills outstanding work – Without automatic process restarts, crashes lead to service unavailability ● With restarts, a hacker may continue trying. ● We shouldn't be scared of core dumps. – When a dog poops inside the house, we don't just `rm -f $poo` or let it pile up, we try to figure out why or how to avoid it again. What is a core dump? ● It's just a file that contains virtual memory contents, register values, and other meta-data. – User land core dump: Represents state of a particular process (e.g. from crash) – Kernel core dump: Represents state of the kernel (e.g. from panic) and process data ● ELF-formatted file (like a program) User Land User Land Crash core Process 1 Process N Kernel Panic vmcore What is Virtual Memory? ● Virtual Memory is an abstraction over physical memory (RAM/swap) – Simplifies programming – User land: process isolation – Kernel/processor translate virtual address references to physical memory locations 64-bit Process Virtual 8GB RAM Address Space (16EB) (Example) 0 0 16 8 EB GB How much virtual memory is used? ● Use `ps` or similar tools to query user process virtual memory usage (in KB): – $ ps -o pid,vsz,rss -p 14062 PID VSZ RSS 14062 44648 42508 Process 1 Virtual 8GB RAM Memory Usage (VSZ) (Example) 0 0 Resident Page 1 Resident Page 2 16 8 EB GB Process 2 How much virtual memory is used? ● Virtual memory is broken up into virtual memory areas (VMAs), the sum of which equal VSZ and may be printed with: – $ cat /proc/${PID}/smaps 00400000-0040b000 r-xp 00000000 fd:02 22151273 /bin/cat Size: 44 kB Rss: 20 kB Pss: 12 kB..
    [Show full text]