1 / 56

Linux+ Guide to Linux Certification, Third Edition

Chapter 14 Troubleshooting, Performance, and Security. Linux+ Guide to Linux Certification, Third Edition. Objectives. Describe and outline good troubleshooting practices Effectively troubleshoot common hardware- and software-related problems

phiala
Download Presentation

Linux+ Guide to Linux Certification, Third Edition

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 14 Troubleshooting, Performance, and Security Linux+ Guide to Linux Certification, Third Edition

  2. Objectives • Describe and outline good troubleshooting practices • Effectively troubleshoot common hardware- and software-related problems • Monitor system performance using command-line and graphical utilities • Identify and fix common performance problems Linux+ Guide to Linux Certification, 3e

  3. Objectives (continued) • Describe the different facets of Linux security • Increase the security of a Linux computer • Outline measures and utilities that can be used to detect a Linux security breach Linux+ Guide to Linux Certification, 3e

  4. Troubleshooting Methodology Figure 14-1: The maintenance cycle Linux+ Guide to Linux Certification, 3e

  5. Troubleshooting Methodology (continued) • Monitoring: observing log files and running performance utilities system to identify problems and their causes • Proactive maintenance: minimizing chance of future problems • e.g., perform regular system backups Linux+ Guide to Linux Certification, 3e

  6. Troubleshooting Methodology (continued) • Reactive maintenance: correcting problems when they arise • Documenting solutions • Developing better proactive maintenance methods • Documentation: system information stored in a log book for future references • All maintenance actions should be documented • Troubleshooting procedures: tasks performed when solving system problems Linux+ Guide to Linux Certification, 3e

  7. Troubleshooting Methodology (continued) Figure 14-2: Common troubleshooting procedures Linux+ Guide to Linux Certification, 3e

  8. Troubleshooting Methodology (continued) • Two troubleshooting golden rules: • Prioritize problems according to severity • Spend reasonable amount of time on each problem given its priority • Ask for help if you can’t solve the problem • Try to solve the root of the problem • Avoid missing underlying cause • Justify why a certain solution is successful Linux+ Guide to Linux Certification, 3e

  9. Resolving Common System Problems • Three categories of problems: • Hardware-related • Software-related • User interface-related Linux+ Guide to Linux Certification, 3e

  10. Hardware-Related Problems • Often involve improper hardware or software configuration • SCSI termination • Video card and monitor configuration • All hardware is on Hardware Compatibility List • POST test alerts • Loose hardware connections • Problems specific to the type of hardware • View output of dmesg command • View content of /var/log/boot.log, /var/log/messages Linux+ Guide to Linux Certification, 3e

  11. Hardware-Related Problems (continued) • Absence of device drivers prevent OS from using associated devices • dmesg command: displays the hardware that is detected by the Linux kernel • lsusb command: displays a list of USB devices detected by the Linux kernel • lspci command: displays a list of PCI devices detected by the Linux kernel • Compare outputs of commands to output of lsmodto determine if driver module is missing from kernel Linux+ Guide to Linux Certification, 3e

  12. Hardware-Related Problems (continued) • Hardware failure can render a device unusable • HDDs most common hardware components to fail • If HDD containing partitions mounted on noncritical directories fails: • Power down computer and replace failed HDD • Boot Linux system • Use fdisk to create partitions on replaced HDD • Use mkfs to create filesystems • Restore original data • Ensure /etc/fstab has appropriate entries to mount filesystems Linux+ Guide to Linux Certification, 3e

  13. Hardware-Related Problems (continued) • If HDD containing / filesystem fails: • Power down computer and replace failed HDD • Reinstall Linux on new HDD • Restore original configuration and data files Linux+ Guide to Linux Certification, 3e

  14. Software-Related Problems:Application-Related Problems • Missing program libraries/files, process restrictions, or conflicting applications • Dependencies: prerequisite shared libraries or packages required for program execution • Programs usually check at installation • Package files may be removed accidentally Linux+ Guide to Linux Certification, 3e

  15. Software-Related Problems:Application-Related Problems (continued) • rpm –V command: identify missing files in a package or package dependency • ldd command: display shared libraries used by a program • ldconfig command: updates list of shared library directories (/etc/ld.so.conf) and list of shared libraries (/etc/ld.so.cache) Linux+ Guide to Linux Certification, 3e

  16. Software-Related Problems:Application-Related Problems (continued) • Too many running processes • Solve by killing parent process of zombie processes • Filehandles: connections programs make to files • ulimit command: modify process limit parameters in current shell • Can also modify max number of filehandles Linux+ Guide to Linux Certification, 3e

  17. Software-Related Problems:Application-Related Problems (continued) • /var/log directory: contains most system log files • Some are hard linked to /var/log directory • If applications stop functioning due to difficulty gaining resources, restart using SIGHUP • Do determine if another process trying to access the same resources attempt to start application in Single User Mode • If resource conflict is the cause of the problem, download newer version of application or application fix Linux+ Guide to Linux Certification, 3e

  18. Software-Related Problems:Operating System-Related Problems • Most software-related problems related to OS • X windows, boot loader, and filesystem problems • Problem detecting video card or monitors by the kernel • To isolate problem starting X Windows or gdm: • View /var/log/Xorg.0.log file • Execute xwininfo or xdpyinfo Linux+ Guide to Linux Certification, 3e

  19. Software-Related Problems:OS-Related Problems (continued) • LILO problems: place “linear” in, remove “compact” from /etc/lilo.conf file • GRUB problems: typically result of missing files in /boot directory • Ensure Linux kernel resides before 1024th cylinder and lba32 keyword is in configuration file • Eliminates BIOS problems with large HDDs Linux+ Guide to Linux Certification, 3e

  20. Software-Related Problems:OS-Related Problems (continued) • If filesystem on partition mounted to noncritical directory becomes corrupted: • Unmount filesystem • Run fsck command with –f (full) option • If fsck command cannot repair filesystem, use mkfs command to re-create the filesystem • Restore filesystem’s original data Linux+ Guide to Linux Certification, 3e

  21. Software-Related Problems:OS-Related Problems (continued) • If / filesystem is corrupted: • Boot from Fedora installation media and enter System Rescue • At shell prompt within System Rescue: • Use mkfs to recreate the filesystem • Use backup utility to restore original data to the re-created / filesystem • Exit System Rescue and reboot system • Knoppix Linux and BBC Linux: bootable Linux distributions with many filesystem repair utilities Linux+ Guide to Linux Certification, 3e

  22. Software-Related Problems: User Interface-Related Problems • Assistive technologies: tools that users can use to modify their desktop experience • Assistive Technologies Preference utility within GNOME Desktop Environment • Preferred Applications to configure Web browser, multimedia player and terminal applications to be opened automatically • Mouse Accessibility to configure speed and click behavior • Keyboard Accessibility to configure keyboard related assistive technologies Linux+ Guide to Linux Certification, 3e

  23. Software-Related Problems: User Interface-Related Problems (continued) Figure 14-3: The Assistive Technologies Preferences utility Linux+ Guide to Linux Certification, 3e

  24. Performance Monitoring • Jabbering: failing hardware components send large amounts of information to CPU • Other causes of poor performance: • Software monopolizes system resources • Too many processes • Too many read/write requests to HDD • Rogue processes Linux+ Guide to Linux Certification, 3e

  25. Performance Monitoring (continued) • To solve software performance issues: • Remove software from the system • Move software to another Linux system • Add CPU or otherwise alter hardware • Bus mastering: peripheral components perform tasks normally executed by CPU Linux+ Guide to Linux Certification, 3e

  26. Performance Monitoring (continued) • To increase performance: • Add RAM • Upgrade to faster HDDs • Disk Striping RAID • Keep CD/DVD drives on a separate HDD controller • Run performance utilities on a regular basis • Record results in a system log book • Eases identification of performance problems • Baseline: measure of normal system activity Linux+ Guide to Linux Certification, 3e

  27. Monitoring Performance with sysstat Utilities • System Statistics (sysstat) package: contains wide range of system monitoring utilities • Use yum install sysstat command to install • mpstat(multiple processor statistics) command: displays CPU statistics • Used to monitor CPU performance • Can specify interval and number of measurements rather than displaying average values • %sys should be smaller than %usr and %nice combined Linux+ Guide to Linux Certification, 3e

  28. Monitoring Performance with sysstat Utilities (continued) • iostat(Input/Output Statistics) command: measures flow of information to and from disk devices • Displays CPU statistics similar to mpstat • Displays statistics for each disk device on the system • Output includes: • Transfers per second • Number of blocks read and written per second • Total number of blocks read and written for the device Linux+ Guide to Linux Certification, 3e

  29. Monitoring Performance with sysstat Utilities (continued) • sar (System Activity Reporter) command: displays various system statistics taken in the last day • Provides more information than mpstat and iostat • By default scheduled to run every 10 minutes • Output logged to a file in /var/log/sa directory • -f option: View statistics from a specific file • Can be used to take current system measurements Linux+ Guide to Linux Certification, 3e

  30. Monitoring Performance with sysstat Utilities (continued) • Additional sar options: • -q option: Displays processor queue statistics • runq -sz value: Number of processes waiting for execution on processor run queue • plist -sz value: Indicates number of processes currently running • ldavg values: Represent average CPU load • -W option: Displays number of pages sent to and taken from swap partition • Large number causes slower performance • Add RAM to resolve Linux+ Guide to Linux Certification, 3e

  31. Monitoring Performance with sysstat Utilities (continued) Table 14-1: Common options to the sar command Linux+ Guide to Linux Certification, 3e

  32. Other Performance Monitoring Utilities • top command: displays CPU statistics, swap usage, memory usage and average CPU load • free command: displays total amounts of physical and swap memory and their utilizations • Can be used to indicate whether more physical memory is required • vmstat command: displays memory, CPU, and swap statistics • Can be used to indicate whether more physical memory is required Linux+ Guide to Linux Certification, 3e

  33. Security • Linux systems typically made available across networks such as the Internet • More prone to security loopholes and attacks • Should improve local and network security • Understand how to detect intruders who breach the system Linux+ Guide to Linux Certification, 3e

  34. Securing the Local Computer • Limit access to physical computer itself • Prevent malicious users from accessing files by directly booting the computer with their own device • Server closet: secured room to store servers • Remove floppy, CD, and DVD drives from workstations • Ensure BIOS prevents booting from USB ports Linux+ Guide to Linux Certification, 3e

  35. Securing the Local Computer (continued) • Ensure BIOS password is set • Set boot loader password in LILO or GRUB configuration file • Prevents intruder from interacting with boot loader • Limit access to graphical desktops and shells • Exit command-line shell before leaving computer • nohup command: prevents background processes from being killed when parent shell is killed or exited • Lock screen using GNOME or KDE Linux+ Guide to Linux Certification, 3e

  36. Securing the Local Computer (continued) • Minimize root user’s time logged in • su (switch user) command: switch current user account to another • Used to switch between root user and regular user • sudo command: perform commands as another user if you have the rights to do that listed in /etc/sudoers file Linux+ Guide to Linux Certification, 3e

  37. Protecting Against Network Attacks • Always a possibility that hackers can manipulate a network service by interacting with it in unusual ways • Buffer overrun: program information for a network service altered in memory Linux+ Guide to Linux Certification, 3e

  38. Network Security Essentials • Minimize number of running network services • nmap (network mapper) command: scans ports on network computers • User can determine what network services are running • Ensure that services that are not needed are not automatically started when entering the runlevel Linux+ Guide to Linux Certification, 3e

  39. Network Security Essentials (continued) • Ensure network service daemons for essential services not run as root user when possible • Ensure that shell listed in /etc/passwd for daemons is set to /sbin/nologin • Hacker will not be able to get BASH shell • New network service versions usually include fixes for known network attacks • Keep network services up-to-date Linux+ Guide to Linux Certification, 3e

  40. Network Security Essentials (continued) • TCP wrapper: program that can start a network daemon • Checks /etc/hosts.allow and /etc/hosts.deny files before starting a network daemon • Examine permissions for files and directories associated with system and network services Linux+ Guide to Linux Certification, 3e

  41. Configuring a Firewall • netfilter/iptables: used to configure a firewall • Discard network packets according to chains of rules • Chains: specify general type of network traffic to apply rules to • Rules: match network traffic to be allowed or dropped • Three chain types: • INPUT: incoming packets • FORWARD: packets passing through computer • OUTPUT chain: outgoing packets Linux+ Guide to Linux Certification, 3e

  42. Configuring a Firewall (continued) • iptables command: creates rules for a chain • Can be based on source IP, destination IP, protocol used, or packet status • Stateful packet filter: Remembers traffic allowed in an existing session and adjust rules appropriately • Easier to use graphical utility to configure firewalls Linux+ Guide to Linux Certification, 3e

  43. Table 14-2: Common iptables options Linux+ Guide to Linux Certification, 3e

  44. Configuring a Firewall (continued) Figure 14-4: The Firewall Configuration utility Linux+ Guide to Linux Certification, 3e

  45. Configuring SELinux • SELinux: Security Enhanced Linux • By default, configured and enabled during Fedora installation • Series of kernel patches and utilities created by NSA • Enforces role-based security • To enable, edit /etc/selinux/config file • Configure SELINUXTYPE option • Reboot and relabel the system • sestatus command: view current SELinux status Linux+ Guide to Linux Certification, 3e

  46. Using Encryption to Protect Network Data • Use encryption algorithms to protect data before it is transmitted on a network • Asymmetric encryption: uses a pair of keys uniquely generated on each system • Public key: freely distributed • Private key: used only by the system, never distributed • Can be used to authenticate messages • Digital signature: message that has been encrypted using a private key Linux+ Guide to Linux Certification, 3e

  47. Working with SSH • By default, SSH uses RSA to encrypt data and DSA to digitally sign data • System wide RSA and DSA key pairs are generated the first time SSH daemon is started • Tunneling: enclosing network traffic within encrypted SSH packets • SSH identity: used to automatically authenticate to other computers using digital signatures • Manage keys using Password and Encryption Keys utility Linux+ Guide to Linux Certification, 3e

  48. Working with SSH (continued) Figure 14-5: The Passwords and Encryption Keys utility Linux+ Guide to Linux Certification, 3e

  49. Working with GPG • Open source version of PGP • Each user has a key pair used for encryption and authentication • Authentication uses trust model • Typically uses RSA and DSA key pairs for asymmetric encryption and digital signing • Can manage GPG keys and encrypt data using: • gpg command • Graphical utility such as Passwords and Encryption Keys utility Linux+ Guide to Linux Certification, 3e

  50. Detecting Intrusion • Log files can contain information or irregularities indicating an intrusion • Review log files in /var/log associated with network services • At minimum, review system log files associated with authentication • Pluggable Authentication Module (PAM): handles authentication requests by network applications • Log file in /var/log/secure Linux+ Guide to Linux Certification, 3e

More Related