Certification general study notes

certification exams will ask questions in less than obvious ways, you must understand the concepts ---------------- General Linux info: 1) LINUX consists of FILES and PROCESSES 2) LINUX is case sensitive 3) LINUX is not going to tell you that you screwed up or that you're an idiot, you'll figure it out on your own. 4) LINUX is silent (see #3) in most cases - therefore TEST commands BEFORE doing them on things you care about. 5) LINUX is terse, compact and efficient. Commands are going to be missing vowels or letters, get over it. 6) LINUX will continue to support LEGACY commands, but will often let you know they are deprecated. 7) The vi editor will always be there for you, it is called "v" "i". 8) a GUI interface is What You See is ALL you Get (Brian Kernighan) - it is limited and limited in power. 9) Because of #2 there are as many as 52 options with letters alone for commands, learn to use man or --help -------------------------- The Linux filesystem tree is based on / which is called root. Under root (or slash) are several directories. -------------------------------------------------------------------- bin - binaries/commands - often linked to /usr/bin - legacy support boot - location of Kernels, image files, boot up configurations and startup details dev - device files - device drivers, special files both block and character, disks, terminals, keyboards, etc. etc - et cetera... a place for ALL the system configuration files including Apache, Postfix, repositories, etc. home - user's home directories lib lib64 - libraries for system, often application libraries will be installed under /usr/lib or /opt/lib lost+found - a special directory to maintain the file systems - do not use media - used to mount CDROM, USB or other temporary devices mnt - can be used to mount devices, legacy use, automount of USB may use /media or /run opt - optional s/w, may contain add on s/w or local software - YMMV proc - files representing processes, including PIDs and system tasks root - root user's home directory run - files representing processes or values of system states sbin - binaries/commands (for root or system level use) selinux - security linux related - not always present srv - various server/service related functions e.g. ftp, www, etc. sys - a variety of files representing system processes or values tmp - temporary directory usr - system commands, files and libraries, typical: /usr/bin, /usr/lib, /usr/sbin, etc. var - log files, spools for mail and cron ----------------------------------------------------- The common directories are categorized as follows: ----------------------------------------------------- COMMANDS will often be found in: /bin /sbin /usr/bin /usr/sbin they may also be found in: /opt or /opt/bin ------------ LIBRARIES and Modules for the system and applications: /lib /usr/lib and sometimes /opt/lib ------------ KERNEL and Bootup files found in: /boot (some config details of course in /etc) ------------ SYSTEM LOG FILES AND SPOOLS for printing and cron are found in: /var ------------ Because Linux consists of FILES and PROCESSES, several directories create place holder files with zero bytes that can be viewed using "cat" to see system processes and details, these directories are: /media /proc /run /srv /sys ---------------- ---------------- Shell related: global configurations are kept in /etc; user specific in ~/ (home) ---------------- in the /etc directory there will be global configuration files for the shell for all users, e.g. /etc/bashrc or /etc/profile in addition there will be templates for new users often found in /etc/skel in a user's home directory there will often be a .profile and/or a .bashrc a home directory is often referred to with ~/ (tilde) a user that is permitted to login will have their customizations in their home directory, any non-login shell related configurations would be located under /etc along with other configuration files for the system. HOWEVEVER, when user logs in, first the system /etc/bash related configuration will be invoked, and THEN any local user configurations will be invoked... so /etc/bashrc and ~/.bashrc are used. basic user account details are found in /etc/passwd - a six field : delimited file, the actual encrypted string for the password is found in /etc/shadow - the file contains passwd aging details. group information is found in /etc/group limits on passwd aging, UID and GID values may be found in /etc/login.defs useradd and adduser both add users - see man pages commands such as usermod, groupadd and other related commands update files via scripts, but changes can be made manually. ---------------- Help related: man, --help, info , man -k , and apropos ---------------- the default help in Linux is the "man" pages, in newer releases of Linux with advanced GNU tools there are also the "--help" option. In addition, some distributions will have "info". one can also use "apropos" or man -k is configured. There are no help commands. ---------------- the vi editor: remember basic navigation... h, j, k, l LEFT, DOWN, UP, RIGHT puts you in command mode, hitting letters to insert or append include: i,I, a, A, o, O and may also include the "insert" key - YMMV to save, type :w to save and quit, hit the escape key, then colon (:), then w and q or :wq to quit out without saving you need to do a q bang or: :q! one does not spell out commands in the ex editor (that's the editor found when you hit :) There are other ways of using commands, not commonly used - see man vi ----------------------- FILE PERMISSIONS: -rwxrwxrwx -421421421 -uuugggooo where r=read (4), w=write (2), and x=execute(1) where u = user (or owner), g = group, and o = other (or world) to change permission specify the desired OCTAL value, for instance, if I want to be able to read and edit a file, and have those in my group read a file, but not others then I would: chmod 640 To make that file executable for me and my group only: chmod 750 http://linuxmeister.net/Notes/chmod-n-other-cmds.html ------------------------- FILE OWNERSHIP: chown username file to also change group, then chown username:groupname file or chgrp groupname file to do an entire directory: chown -R username:groupname directory (or wildcards within a directory) ------------------------- scripting notes: first line is a shell directive, tells the shell to execute commands from this file based on a shell or env, e.g. #!/bin/bash would execute all commands in that file as under a bash shell (normal). when testing conditions one compares values using boolean expressions or numeric values. If you seek to have a negative condition you'd use a "bang" ! to negate you can establish a case where you test, if certain conditions exist then certain actions take place. you can evaluate various conditions of variables using "for", e.g. for the files in a list, then, do this while, or until... when in a do loop you can test for and do something: while - a particular condition exists or until - a particular condition exists or doesn't exist (say a numeric value is reached or a file is created) if you want to pause a script until someone enters data or hits return, use "read" To make a script execute one may:~/filename 1) execute the script with normal permissions by typing: sh ./filename 2) chmod 744 filename, then execute by typing 3) first chmod and then include ~/ in path env, then type: filename 4) to test if path and execute bits are set, test by: which filename -if found, it'll work ------------------------- /etc/hosts - records local IP addresses - is necessary for the loopback /etc/resolv.conf has the name search path and nameserver info, it is often controlled by /etc/sysconfig/network files /etc/nsswitch.conf points to centralized services or files ------------------------- The following are the basics of networking, assuming a private, non-routable network of The router address would be The network subnet mask is The broadcast ping address is ------------------------------------------------ The local system MUST have an internal loopback address of and it MUST be in /etc/hosts The local system's IP address will be assigned to the network interface: ------------------------------------------------ The network commands are: ifconfig, ping, route, hostname, traceroute, nslookup ------------------------------------------------ # done as root user or using sudo: # configure device name, IP, netmask, broadcast ifconfig lan0 netmask broadcast # configure default route # add default gateway route add default gw # IF the system configuration files are correct one can use ifup and ifdown on an interface. ------------------------------------------------ /etc/sudoers allows users to either execute specific commands as root, or become root without the root passwd. to add or edit: visudo is the preferred tool ------------------------------------------------ filesystems and drives are managed using fdisk is the drive is less than 2TB, if greater than 2TB one will use parted or gdisk - GPT fdisk (gdisk) version 0.8.7 ------------------------------------------------ -> chkconfig --help usage: chkconfig -A|--allservices (together with -l: show all services) chkconfig -t|--terse [names] (shows the links) chkconfig -e|--edit [names] (configure services) chkconfig -s|--set [name state]... (configure services) chkconfig -l|--list [--deps] [names] (shows the links) chkconfig -c|--check name [state] (check state) chkconfig -a|--add [names] (runs insserv) chkconfig -d|--del [names] (runs insserv -r) chkconfig -h|--help (print usage) chkconfig -f|--force ... (call insserv with -f) chkconfig [name] same as chkconfig -t chkconfig name state... same as chkconfig -s name state chkconfig --root= ... use as the root file system ------------------------------------------------ -> systemctl --help systemctl [OPTIONS...] {COMMAND} ... Query or send control commands to the systemd manager. -h --help Show this help --version Show package version -t --type=TYPE List only units of a particular type --state=STATE List only units with particular LOAD or SUB or ACTIVE state -p --property=NAME Show only properties by this name -a --all Show all loaded units/properties, including dead/empty ones. To list all units installed on the system, use the 'list-unit-files' command instead. --reverse Show reverse dependencies with 'list-dependencies' -l --full Don't ellipsize unit names on output --fail When queueing a new job, fail if conflicting jobs are pending --irreversible When queueing a new job, make sure it cannot be implicitly cancelled --ignore-dependencies When queueing a new job, ignore all its dependencies --show-types When showing sockets, explicitly show their type -i --ignore-inhibitors When shutting down or sleeping, ignore inhibitors --kill-who=WHO Who to send signal to -s --signal=SIGNAL Which signal to send -H --host=[USER@]HOST Show information for remote host -P --privileged Acquire privileges before execution -q --quiet Suppress output --no-block Do not wait until operation finished --no-wall Don't send wall message before halt/power-off/reboot --no-reload When enabling/disabling unit files, don't reload daemon configuration --no-legend Do not print a legend (column headers and hints) --no-pager Do not pipe output into a pager --no-ask-password Do not ask for system passwords --system Connect to system manager --user Connect to user service manager --global Enable/disable unit files globally --runtime Enable unit files only temporarily until next reboot -f --force When enabling unit files, override existing symlinks When shutting down, execute action immediately --root=PATH Enable unit files in the specified root directory -n --lines=INTEGER Numer of journal entries to show -o --output=STRING Change journal output mode (short, short-monotonic, verbose, export, json, json-pretty, json-sse, cat) Unit Commands: list-units List loaded units list-sockets List loaded sockets ordered by address start [NAME...] Start (activate) one or more units stop [NAME...] Stop (deactivate) one or more units reload [NAME...] Reload one or more units restart [NAME...] Start or restart one or more units try-restart [NAME...] Restart one or more units if active reload-or-restart [NAME...] Reload one or more units if possible, otherwise start or restart reload-or-try-restart [NAME...] Reload one or more units if possible, otherwise restart if active isolate [NAME] Start one unit and stop all others kill [NAME...] Send signal to processes of a unit is-active [NAME...] Check whether units are active is-failed [NAME...] Check whether units are failed status [NAME...|PID...] Show runtime status of one or more units show [NAME...|JOB...] Show properties of one or more units/jobs or the manager set-property [NAME] [ASSIGNMENT...] Sets one or more properties of a unit help [NAME...|PID...] Show manual for one or more units reset-failed [NAME...] Reset failed state for all, one, or more units list-dependencies [NAME] Recursively show units which are required or wanted by this unit or by which this unit is required or wanted Unit File Commands: list-unit-files List installed unit files enable [NAME...] Enable one or more unit files disable [NAME...] Disable one or more unit files reenable [NAME...] Reenable one or more unit files preset [NAME...] Enable/disable one or more unit files based on preset configuration is-enabled [NAME...] Check whether unit files are enabled mask [NAME...] Mask one or more units unmask [NAME...] Unmask one or more units link [PATH...] Link one or more units files into the search path get-default Get the name of the default target set-default NAME Set the default target Job Commands: list-jobs List jobs cancel [JOB...] Cancel all, one, or more jobs Snapshot Commands: snapshot [NAME] Create a snapshot delete [NAME...] Remove one or more snapshots Environment Commands: show-environment Dump environment set-environment [NAME=VALUE...] Set one or more environment variables unset-environment [NAME...] Unset one or more environment variables Manager Lifecycle Commands: daemon-reload Reload systemd manager configuration daemon-reexec Reexecute systemd manager System Commands: default Enter system default mode rescue Enter system rescue mode emergency Enter system emergency mode halt Shut down and halt the system poweroff Shut down and power-off the system reboot Shut down and reboot the system kexec Shut down and reboot the system with kexec exit Request user instance exit switch-root [ROOT] [INIT] Change to a different root file system suspend Suspend the system hibernate Hibernate the system hybrid-sleep Hibernate and suspend the system ----------------------------------- setting up a filesystem (using LVM as well) http://linuxmeister.net/FileSystems/setup-LVM.html process: - fdisk -l (see: http://linuxmeister.net/FileSystems/newdisk-setup.html ) pvcreate /dev/sd?5 pvdisplay vgcreate vg199 /dev/sd[c-k]5 vgdisplay lvcreate -L 303400 vg199 lvdisplay - mkfs -t ext3 /dev/mapper/vg199-lvol0 - vi /etc/fstab - add: /dev/vg199/lvol0 /VG199 ext3 defaults 0 0 - mkdir /VG199 - mount -a - df -h ----------------------------------- Basic Linux Tasks ------------------------------------------------------------------------- Users - adduser/useradd/userdel - etc:passwd, shadow, group, skel, motd file permissions and ownership - chmod, chown wrapper scripts, date suffix: http://linuxmeister.net/Notes/date-suffix.html create an initrd image - mkinitrd partitions - fdisk, gdisk, parted, /etc/fstab, mount, umount, mnt, media xfs - journaled file system created by SGI for IRIX ext3, ext4 - journaled filesystems mknod option name type major minor (major/minor related to the bus) lspci - PCI busses and peripherals lsusb - usb components find files - find, locate, whereis, which updatedb - locate files using whereis regular expressions - grep, sed, awk http://linuxmeister.net/Notes/sed-examples.html packages - rpm, yum, apt-get, aptitude, zypper, tar network - ifconfig, ip addr, ping, nslookup, traceroute, dig, /etc: hosts, resolv.conf, nsswitch.conf, sysconfig/ Redirection: ----------------------------------------------------- > stdout to a file >> append stdout to end of file 2> stderr to a file, or 2>/dev/null 2>> append stderr to destination file &> all output to a file is 1st value LT 2nd value? = 1st value LT or = to 2nd? sudo cat /etc/sudoers | grep -v ^# | grep -v ^$ Defaults always_set_home Defaults env_reset Defaults env_keep = "LANG LC_ADDRESS LC_CTYPE LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGES LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONE LC_TIME LC_ALL LANGUAGE LINGUAS XDG_SESSION_COOKIE" Defaults !insults Defaults targetpw # ask for the password of the target user i.e. root ALL ALL=(ALL) ALL # WARNING! Only use this together with 'Defaults targetpw'! root ALL=(ALL) ALL luser ALL=(ALL) NOPASSWD: ALL ----------------------------------------------------- for - items in list - do - done ----------------------------------------------------- #!/bin/bash # script with test and loop TOOL="dmesg bootloader ldd ldconfig dpkg dpkg-reconfigure apt-get apt-cache aptitude rpm rpm2cpio yum yumdownloader bash echo env exec export pwd set unset man uname history cat cut expand fmt head od join nl paste pr sed sort split tail tr unexpand uniq wc cp find mkdir mv ls rm rmdir touch tar cpio dd file gzip gunzip bzip2 tee xargs bg fg jobs kill nohup ps top free uptime killall nice ps renice top grep egrep fgrep sed regex vi fdisk mkfs mkswap du df fsck e2fsck mke2fs debugfs dumpe2fs tune2fs mount umount quota edquota repquota quotaon chmod umask chown chgrp find locate updatedb whereis which type" ; export TOOL # TOOL="cd mkdir ls" ; export TOOL # used to test loop # for x in $TOOL do # which $x # if [^$] if [! x] <--- test? # echo "builtin command or not found" # fi man $x | col -b > man.$x.txt done ls -al ----------------------------------------------------- while - while condition exists - do - done http://linuxmeister.net/Scripts/while-loop.sh.html http://linuxmeister.net/Scripts/do-while-count-loop.txt ----------------------------------------------------- until - until condition is satisifed - do - done ----------------------------------------------------- pidof - displays pid of named process pgrep - displays pid of matching process ps command ----------------------------------------------------- PRI - priority - higher numbers, lower priority NI - nice - higher numbers, less CPU time (lowering nice increases time - CAREFUL, system must be higher) SIZE - virtual image size RSS - physical memory in KB WCHAN - kernel function where the process resides STAT - status: R - running, T - terminated (stopped), D - dead (asleep & uninterruptible), S - sleeping, Z - Zombie, N - +nice value TT - tty associated with proc PAGEIN - number of major page faults TRS - resident text size SWAP - KB swap used SHARE - shared memory ----------------------------------------------------- nohup - will keep process going if user is disconnected (think modem) - output to nohup.out bg - background, fg - foreground, jobs, kill at - schedule job at the command line to run at a set time cron - schedule job(s) to occur at specific times, repeatedly... --> crontab -l # DO NOT EDIT THIS FILE - edit the master and reinstall. # (/tmp/crontab.EZv91Z installed on Sun May 10 22:07:58 2015) # (Cronie version 4.2) # MIN HOUR DAY MONTH DAYOFWEEK COMMAND 58 23 * * * /home/luser/bin/mkallavi # 5 6-20 * * * /home/luser/bin/get-map # */2 7-10 * * * /home/luser/bin/get-map # */2 14-18 * * * /home/luser/bin/get-map ----------------------------------------------------- YMMV: /etc/sysconfig - used for configuration files of startup - network items like dns and dhcp should be configured in this directory YMMV: log files: /var/log/messages - SuSE /var/log/syslog - not used on SuSE ----------------------------------------------------- --> sudo cat /etc/rsyslog.conf | grep -v ^# | grep -v ^$ $ModLoad immark.so $MarkMessagePeriod 3600 $ModLoad imuxsock.so $RepeatedMsgReduction on $ModLoad imklog.so $klogConsoleLogLevel 1 $IncludeConfig /var/run/rsyslog/additional-log-sockets.conf $IncludeConfig /etc/rsyslog.d/*.conf if ( \ /* kernel up to warning except of firewall */ \ ($syslogfacility-text == 'kern') and \ ($syslogseverity <= 4 /* warning */ ) and not \ ($msg contains 'IN=' and $msg contains 'OUT=') \ ) or ( \ /* up to errors except of facility authpriv */ \ ($syslogseverity <= 3 /* errors */ ) and not \ ($syslogfacility-text == 'authpriv') \ ) \ then /dev/tty10 & |/dev/xconsole *.emerg :omusrmsg:* if ($syslogfacility-text == 'kern') and \ ($msg contains 'IN=' and $msg contains 'OUT=') \ then -/var/log/firewall & stop if ($programname == 'acpid' or $syslogtag == '[acpid]:') and \ ($syslogseverity <= 5 /* notice */) \ then -/var/log/acpid & stop if ($programname == 'NetworkManager') or \ ($programname startswith 'nm-') \ then -/var/log/NetworkManager & stop mail.* -/var/log/mail mail.info -/var/log/mail.info mail.warning -/var/log/mail.warn mail.err /var/log/mail.err news.crit -/var/log/news/news.crit news.err -/var/log/news/news.err news.notice -/var/log/news/news.notice *.=warning;*.=err -/var/log/warn *.crit /var/log/warn *.*;mail.none;news.none -/var/log/messages local0.*;local1.* -/var/log/localmessages local2.*;local3.* -/var/log/localmessages local4.*;local5.* -/var/log/localmessages local6.*;local7.* -/var/log/localmessages ------------------------------------------------------------------ Non-Routable - Private IP ranges: https://tools.ietf.org/html/rfc1918 RFC 1918 Address Allocation for Private Internets February 1996 3. Private Address Space The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets: - (10/8 prefix) - (172.16/12 prefix) - (192.168/16 prefix) We will refer to the first block as "24-bit block", the second as "20-bit block", and to the third as "16-bit" block. Note that (in pre-CIDR notation) the first block is nothing but a single class A network number, while the second block is a set of 16 contiguous class B network numbers, and third block is a set of 256 contiguous class C network numbers. ------------------------------------------------------------------

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