This post is about some of the basic unix/linux commands, there is also a sequel to it.
chapter 1 => unix runlevel [0 to 6]
A run level is a state of init and the whole system that defines what system services are operating.
run-level 2 = Local Multiuser with Networking but without network service (like NFS)
similarly my amazon elastic cloud VM was on runlevel 3, which means Multi-user mode with networking.
The /etc/inittab will use the file /etc/rc<RUN_LEVEL>.d/
Read more about 4.2. Boot process, Init and shutdown
display the unit file that systemd has loaded into its system, systemctl cat docker.service and do list the dependencies of the service systemctl list-dependencies docker.service
chapter 3 => linux processes
Linux process is a "dynamic entity", constantly changing as the machine code instructions are executed by the processor. As well as the program's instructions and data, the process also includes the program counter and all of the CPU's registers as well as the process stacks containing temporary data such as routine parameters, return addresses and saved variables. The current executing program, or process, includes all of the current activity in the microprocessor.
Modern virtual memory operating systems generally have a flat memory model and not a segmented one.
List all linux processes,
List all running linux processes,
To kill a process,
The memory is virtualized among the processes on the system. An individual process's view of memory is as if it alone has full access to the system's physical memory.
Read more about linux process, and process virtual address space
chapter 4 => 32 or 64 bit OS
In 32-bit, a processor with 32-bit memory addresses can directly access at most (2^32) bits = 4 GiB of byte-addressable memory.
Which also means, each register stores 32 bits = 4 bytes. 32 bits (1 word) of information are processed per clock cycle.
In 64-bit computing, processors that have datapath widths, integer size, and memory-address widths of 64 bits = 8 bytes.
Which also means, each register stores 64 bits = 8 bytes. 64 bits (1 word) of information are processed per clock cycle.
or
ELF - https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
LSB is Linux Standard Base including fs - https://en.wikipedia.org/wiki/Linux_Standard_Base
Watch this for more info, 32 Bit vs 64 Bit - How much data the OS can handle
OS
chapter 5 => linux access control/user groups
user groups are defined in /etc/group
To know which group the current user is assigned to,
To know the groups, current user assigned to with the group id/gid, which you can map in /etc/group
Similarly, all users are defined in /etc/passwd.
Read this for user management.
chapter 6 => package repos and PPA (package archives)
On rh,
On ubuntu,
chapter 7 => task scheduling
When I check the /etc/cron.daily in RHEL 7 I get a following list of bash files.
And on ubuntu distro,
One of them, /etc/cron.daily/apt does variety of things based on apt configuration settings, which are maintained in /etc/apt/apt.conf and the various include files under /etc/apt/apt.conf.d/
The /etc/apt is something like this :
chapter 8 => network proxy
specify system-wide environment variables http_proxy and https_proxy as below,
Read about Networking and proxy server.
SOCKet Secure (SOCKS) is an Internet protocol that routes network packets between a client and server through a proxy-server.
I also can add env variables to /etc/profile and source it to see immediate effect.
chapter 9 => sudo version
chapter 10 => Install packages (ubuntu)
prayag@prayag:~/Downloads$ sudo dpkg -i TrackerSetup.deb
Or with gDEBi,
prayag@prayag:~/Downloads$ sudo apt-get install gdebi
prayag@prayag:~/Downloads$ sudo gdebi TrackerSetup.deb
check about the installed package
prayag@prayag:~/Downloads$ dpkg -s gedit
http://askubuntu.com/a/17829/37643
chapter 11 => play popular non-free media formats (ubuntu)
sudo apt-get install ubuntu-restricted-extras
sudo apt-get install libavcodec-extra-53 libavcodec53 ffmpeg
References
How to install REALVNC gui in ubuntu 12.04?
How can I specify a display?
Installing & Running VNC on Redhat/RPM Linux
Starting firefox on a remote host (over ssh) opens a new window locally: what is happening?
visit url with command line
http://waxborg.servepics.com/opensuse/remote-administration/running-firefox-remotely-over-ssh
How to shut down the computer after a task has been completed?, http://askubuntu.com/a/15536
How can I install software or packages without Internet (offline)?
35 Tricky and Complex Unix Interview Questions and Commands (Part 1)
Linux Hacks gist, https://gist.github.com/prayagupd/4730009
chapter 1 => unix runlevel [0 to 6]
A run level is a state of init and the whole system that defines what system services are operating.
prayag@prayag_f1:~$ who -r
run-level 2 2012-12-09 17:04
run-level 2 = Local Multiuser with Networking but without network service (like NFS)
similarly my amazon elastic cloud VM was on runlevel 3, which means Multi-user mode with networking.
So, once the kernel is loaded, it finds init in sbin and executes it.
ll /sbin/init lrwxrwxrwx 1 root root 20 Sep 28 18:40 /sbin/init -> /lib/systemd/systemd*Then init continues to read the /etc/inittab file (/etc/init.d in ubuntu), which describes how the system should be set up in each run-level and sets the default run-level.
The /etc/inittab will use the file /etc/rc<RUN_LEVEL>.d/
ll /etc/rc2.d/ total 20 drwxr-xr-x 2 root root 4096 Nov 12 12:58 ./ drwxr-xr-x 132 root root 12288 Nov 12 12:58 ../ -rw-r--r-- 1 root root 677 Feb 5 2016 README lrwxrwxrwx 1 root root 16 Nov 11 14:12 S01apport -> ../init.d/apport* lrwxrwxrwx 1 root root 17 Nov 11 14:12 S01rsyslog -> ../init.d/rsyslog* lrwxrwxrwx 1 root root 15 Nov 11 14:12 S01uuidd -> ../init.d/uuidd* lrwxrwxrwx 1 root root 15 Nov 11 14:12 S02acpid -> ../init.d/acpid* lrwxrwxrwx 1 root root 17 Nov 11 14:12 S02anacron -> ../init.d/anacron* lrwxrwxrwx 1 root root 24 Nov 12 12:58 S02cgroupfs-mount -> ../init.d/cgroupfs-mount* lrwxrwxrwx 1 root root 14 Nov 11 14:12 S02cron -> ../init.d/cron* lrwxrwxrwx 1 root root 14 Nov 11 14:12 S02dbus -> ../init.d/dbus* lrwxrwxrwx 1 root root 20 Nov 11 14:12 S02irqbalance -> ../init.d/irqbalance* lrwxrwxrwx 1 root root 20 Nov 11 14:12 S02kerneloops -> ../init.d/kerneloops* lrwxrwxrwx 1 root root 15 Nov 11 14:12 S02rsync -> ../init.d/rsync* lrwxrwxrwx 1 root root 27 Nov 11 14:12 S02speech-dispatcher -> ../init.d/speech-dispatcher* lrwxrwxrwx 1 root root 18 Nov 11 14:12 S02thermald -> ../init.d/thermald* lrwxrwxrwx 1 root root 18 Nov 11 14:12 S02whoopsie -> ../init.d/whoopsie* lrwxrwxrwx 1 root root 22 Nov 11 14:12 S03avahi-daemon -> ../init.d/avahi-daemon* lrwxrwxrwx 1 root root 19 Nov 11 14:12 S03bluetooth -> ../init.d/bluetooth* lrwxrwxrwx 1 root root 16 Nov 12 12:58 S03docker -> ../init.d/docker* lrwxrwxrwx 1 root root 17 Nov 11 14:12 S03lightdm -> ../init.d/lightdm* lrwxrwxrwx 1 root root 14 Nov 11 14:12 S04cups -> ../init.d/cups* lrwxrwxrwx 1 root root 22 Nov 11 14:12 S04cups-browsed -> ../init.d/cups-browsed* lrwxrwxrwx 1 root root 15 Nov 11 14:12 S04saned -> ../init.d/saned* lrwxrwxrwx 1 root root 21 Nov 11 14:12 S05grub-common -> ../init.d/grub-common* lrwxrwxrwx 1 root root 18 Nov 11 14:12 S05ondemand -> ../init.d/ondemand* lrwxrwxrwx 1 root root 18 Nov 11 14:12 S05plymouth -> ../init.d/plymouth* lrwxrwxrwx 1 root root 18 Nov 11 14:12 S05rc.local -> ../init.d/rc.local*
Read more about 4.2. Boot process, Init and shutdown
chapter 2 => linux system state/ linux services
A Linux service is an app that runs in the background waiting to be used, or carrying out essential tasks. eg. Apache and MySQL.
I will generally be unaware of services until I need them.
System state
-----------------
systemCTL is the central management tool for controlling the init system.
With systemCTL, I can start and stop, enable/disable systemd services.
* The systemctl list-units command only displays units that systemd has attempted to parse and load into memory.
* systemd will only read units that it thinks it needs, this will not necessarily include all of the available units on the system.
* To see every available unit-file within the systemd paths, including those that systemd has not attempted to load, you can use the list-unit-files command instead
A Linux service is an app that runs in the background waiting to be used, or carrying out essential tasks. eg. Apache and MySQL.
I will generally be unaware of services until I need them.
System state
-----------------
systemCTL is the central management tool for controlling the init system.
With systemCTL, I can start and stop, enable/disable systemd services.
* The systemctl list-units command only displays units that systemd has attempted to parse and load into memory.
* systemd will only read units that it thinks it needs, this will not necessarily include all of the available units on the system.
* To see every available unit-file within the systemd paths, including those that systemd has not attempted to load, you can use the list-unit-files command instead
systemctl list-unit-files UNIT FILE STATE proc-sys-fs-binfmt_misc.automount static org.freedesktop.hostname1.busname static org.freedesktop.locale1.busname static org.freedesktop.login1.busname static org.freedesktop.network1.busname static org.freedesktop.resolve1.busname static org.freedesktop.systemd1.busname static org.freedesktop.timedate1.busname static dev-hugepages.mount static dev-mqueue.mount static proc-sys-fs-binfmt_misc.mount static sys-fs-fuse-connections.mount static sys-kernel-config.mount static sys-kernel-debug.mount static acpid.path enabled cups.path enabled systemd-ask-password-console.path static systemd-ask-password-plymouth.path static systemd-ask-password-wall.path static systemd-networkd-resolvconf-update.path static accounts-daemon.service enabled acpid.service disabled docker.service enabled dbus.socket static docker.socket enabled
display the unit file that systemd has loaded into its system, systemctl cat docker.service and do list the dependencies of the service systemctl list-dependencies docker.service
chapter 3 => linux processes
Linux process is a "dynamic entity", constantly changing as the machine code instructions are executed by the processor. As well as the program's instructions and data, the process also includes the program counter and all of the CPU's registers as well as the process stacks containing temporary data such as routine parameters, return addresses and saved variables. The current executing program, or process, includes all of the current activity in the microprocessor.
Modern virtual memory operating systems generally have a flat memory model and not a segmented one.
List all linux processes,
$ ps -A
PID TTY TIME CMD
1 ? 00:00:01 systemd
4142 ? 00:00:02 dockerd
4151 ? 00:00:00 docker-containerd
List all running linux processes,
ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.1 119836 6044 ? Ss 12:54 0:01 /sbin/init splash root 4142 0.0 0.9 419120 37848 ? Ssl 12:58 0:02 /usr/bin/dockerd -H fd:// root 4151 0.0 0.2 199756 10568 ? Ssl 12:58 0:00 docker-containerd -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --shim docker-containerd-shim --metrics-interval=0 --start-timeout 2m --state-dir /var/run/docker/libcontainerd/containerd --runtime docker-runc
To kill a process,
$ pkill vim
The memory is virtualized among the processes on the system. An individual process's view of memory is as if it alone has full access to the system's physical memory.
Read more about linux process, and process virtual address space
chapter 4 => 32 or 64 bit OS
In 32-bit, a processor with 32-bit memory addresses can directly access at most (2^32) bits = 4 GiB of byte-addressable memory.
Which also means, each register stores 32 bits = 4 bytes. 32 bits (1 word) of information are processed per clock cycle.
In 64-bit computing, processors that have datapath widths, integer size, and memory-address widths of 64 bits = 8 bytes.
Which also means, each register stores 64 bits = 8 bytes. 64 bits (1 word) of information are processed per clock cycle.
prayag@prayag_f1:~$ file /sbin/init /sbin/init: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=0x5f722891935c0f35fd8f318d4606b334a9b1d423, stripped
or
[ec2-user@ip-172-21-19-140 ~]$ file /lib/systemd/systemd /lib/systemd/systemd: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=51a025073a1ab8c1a4dfa808d5af7240179400a1, stripped
ELF - https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
LSB is Linux Standard Base including fs - https://en.wikipedia.org/wiki/Linux_Standard_Base
Watch this for more info, 32 Bit vs 64 Bit - How much data the OS can handle
OS
[ec2-user@ip-172-18-21-240 ~]$ cat /proc/version Linux version 3.10.0-514.el7.x86_64 (mockbuild@x86-039.build.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-11) (GCC) ) #1 SMP Wed Oct 19 11:24:13 EDT 2016
chapter 5 => linux access control/user groups
user groups are defined in /etc/group
$ cut -d: -f1 /etc/group root daemon bin sys adm lp uucp man proxy sudo dip sasl plugdev staff games users nogroup input crontab syslog netdev messagebus ssh pulse pulse-access rtkit saned prayagupd sambashare vboxsf docker
To know which group the current user is assigned to,
groups prayagupd adm cdrom sudo dip plugdev lpadmin sambashare vboxsf
or
groups $USER prayagupd : prayagupd adm cdrom sudo dip plugdev lpadmin sambashare vboxsf
To know the groups, current user assigned to with the group id/gid, which you can map in /etc/group
id $USER
uid=1000(prayagupd) gid=1000(prayagupd) groups=1000(prayagupd),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),113(lpadmin),128(sambashare),999(vboxsf)
Similarly, all users are defined in /etc/passwd.
cut -d: -f1 /etc/passwd
Read this for user management.
chapter 6 => package repos and PPA (package archives)
On rh,
[ec2-user@ip-172-0-0-128 ~]$ yum repolist Loaded plugins: extras_suggestions, langpacks, priorities, update-motd repo id repo name status !amzn2-core/2/x86_64 Amazon Linux 2 core repository 16,294 amzn2extra-docker/2/x86_64 Amazon Extras repo for docker 14 docker-ce-stable/x86_64 Docker CE Stable - x86_64 36 repolist: 16,344
On ubuntu,
prayag@prayag_f1:~$ grep ^ /etc/apt/sources.list /etc/apt/sources.list.d/* /etc/apt/sources.list:# deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release i386 (20120423)]/ precise main restricted /etc/apt/sources.list: /etc/apt/sources.list:# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to /etc/apt/sources.list:# newer versions of the distribution. /etc/apt/sources.list:deb http://np.archive.ubuntu.com/ubuntu/ precise main restricted /etc/apt/sources.list:deb-src http://np.archive.ubuntu.com/ubuntu/ precise main restricted [...] /etc/apt/sources.list.d/dropbox.list:deb http://linux.dropbox.com/ubuntu precise main /etc/apt/sources.list.d/dropbox.list.save:deb http://linux.dropbox.com/ubuntu precise main /etc/apt/sources.list.d/google-chrome.list:### THIS FILE IS AUTOMATICALLY CONFIGURED ### /etc/apt/sources.list.d/google-chrome.list:# You may comment out this entry, but any other modifications may be lost. /etc/apt/sources.list.d/google-chrome.list:deb http://dl.google.com/linux/chrome/deb/ stable main /etc/apt/sources.list.d/google-chrome.list.save:### THIS FILE IS AUTOMATICALLY CONFIGURED ### /etc/apt/sources.list.d/google-chrome.list.save:# You may comment out this entry, but any other modifications may be lost. /etc/apt/sources.list.d/google-chrome.list.save:deb http://dl.google.com/linux/chrome/deb/ stable main /etc/apt/sources.list.d/groovy-dev-grails-precise.list:deb http://ppa.launchpad.net/groovy-dev/grails/ubuntu precise main /etc/apt/sources.list.d/groovy-dev-grails-precise.list:deb-src http://ppa.launchpad.net/groovy-dev/grails/ubuntu precise main /etc/apt/sources.list.d/groovy-dev-grails-precise.list.save:deb http://ppa.launchpad.net/groovy-dev/grails/ubuntu precise main /etc/apt/sources.list.d/groovy-dev-grails-precise.list.save:deb-src http://ppa.launchpad.net/groovy-dev/grails/ubuntu precise main /etc/apt/sources.list.d/precise-partner.list:deb http://archive.canonical.com/ubuntu precise partner #Added by software-center /etc/apt/sources.list.d/precise-partner.list.save:deb http://archive.canonical.com/ubuntu precise partner #Added by software-center /etc/apt/sources.list.d/ubuntu-mozilla-daily-ppa-precise.list:deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu precise main /etc/apt/sources.list.d/ubuntu-mozilla-daily-ppa-precise.list:deb-src http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu precise main /etc/apt/sources.list.d/ubuntu-on-rails-ppa-precise.list:deb http://ppa.launchpad.net/ubuntu-on-rails/ppa/ubuntu precise main
chapter 7 => task scheduling
When I check the /etc/cron.daily in RHEL 7 I get a following list of bash files.
[ec2-user@ip-172-21-19-140 ~]$ ll /etc/cron.daily/
total 12
-rwx------. 1 root root 219 Jul 14 2016 logrotate
-rwxr-xr-x. 1 root root 618 Mar 17 2014 man-db.cron
-rwx------. 1 root root 256 Sep 13 2016 rhsmd
And on ubuntu distro,
prayag@prayag_f1:~$ ls -l /etc/cron.daily/
total 64
-rwxr-xr-x 1 root root 311 May 25 2012 0anacron
-rwxr-xr-x 1 root root 219 Oct 1 15:44 apport
-rwxr-xr-x 1 root root 15466 Oct 16 16:44 apt
-rwxr-xr-x 1 root root 355 Jun 19 03:42 bsdmainutils
-rwxr-xr-x 1 root root 384 May 25 2012 cracklib-runtime
-rwxr-xr-x 1 root root 256 Oct 2 01:15 dpkg
-rwxr-xr-x 1 root root 372 Oct 3 04:17 logrotate
-rwxr-xr-x 1 root root 1365 Sep 19 04:29 man-db
-rwxr-xr-x 1 root root 606 Aug 15 09:11 mlocate
-rwxr-xr-x 1 root root 249 Sep 7 00:59 passwd
-rwxr-xr-x 1 root root 2417 Jul 2 2011 popularity-contest
-rwxr-xr-x 1 root root 2947 Jun 15 00:41 standard
-rwxr-xr-x 1 root root 214 Oct 10 04:26 update-notifier-common
One of them, /etc/cron.daily/apt does variety of things based on apt configuration settings, which are maintained in /etc/apt/apt.conf and the various include files under /etc/apt/apt.conf.d/
The /etc/apt is something like this :
#!/bin/sh [...] check_stamp() { stamp="$1" interval="$2" if [ $interval -eq 0 ]; then debug_echo "check_stamp: interval=0" # treat as no time has passed return 1 fi if [ ! -f $stamp ]; then debug_echo "check_stamp: missing time stamp file: $stamp." # treat as enough time has passed return 0 fi # compare midnight today to midnight the day the stamp was updated stamp_file="$stamp" stamp=$(date --date=$(date -r $stamp_file --iso-8601) +%s 2>/dev/null) if [ "$?" != "0" ]; then # Due to some timezones returning 'invalid date' for midnight on # certain dates (eg America/Sao_Paulo), if date returns with error # remove the stamp file and return 0. See coreutils bug: # http://lists.gnu.org/archive/html/bug-coreutils/2007-09/msg00176.html rm -f "$stamp_file" return 0 fi now=$(date --date=$(date --iso-8601) +%s 2>/dev/null) if [ "$?" != "0" ]; then # As above, due to some timezones returning 'invalid date' for midnight # on certain dates (eg America/Sao_Paulo), if date returns with error # return 0. return 0 fi delta=$(($now-$stamp)) # intervall is in days, convert to sec. interval=$(($interval*60*60*24)) debug_echo "check_stamp: interval=$interval, now=$now, stamp=$stamp, delta=$delta (sec)" # remove timestamps a day (or more) in the future and force re-check if [ $stamp -gt $(($now+86400)) ]; then echo "WARNING: file $stamp_file has a timestamp in the future: $stamp" rm -f "$stamp_file" return 0 fi if [ $delta -ge $interval ]; then return 0 fi return 1 } update_stamp() { stamp="$1" touch $stamp } [...]
chapter 8 => network proxy
specify system-wide environment variables http_proxy and https_proxy as below,
prayag@prayag_f1:~$ cat /etc/environment PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games" http_proxy="http://10.xx.xxx.xxx:8080/" https_proxy="https://10.xx.xxx.xxx:8080/" ftp_proxy="ftp://10.xx.xxx.xxx:8080/" socks_proxy="socks://10.xx.xxx.xxx:8080/"
SOCKet Secure (SOCKS) is an Internet protocol that routes network packets between a client and server through a proxy-server.
prayag@prayag_f1:~$ env | grep -i proxy NO_PROXY=localhost,127.0.0.0/8 http_proxy=http://10.xx.xxx.xxx:8080/ ftp_proxy=ftp://10.xx.xxx.xxx:8080/ ALL_PROXY=socks://10.xx.xxx.xxx:8080/ all_proxy=socks://10.xx.xxx.xxx:8080/ socks_proxy=socks://10.xx.xxx.xxx:8080/ UBUNTU_MENUPROXY=libappmenu.so https_proxy=https://10.xx.xxx.xxx:8080/ no_proxy=localhost,127.0.0.0/8
I also can add env variables to /etc/profile and source it to see immediate effect.
chapter 9 => sudo version
prayag@prayag_f1:~$ sudo sudo -V
[...]
Sudoers I/O plugin version 1.8.5p2
chapter 10 => Install packages (ubuntu)
prayag@prayag:~/Downloads$ sudo dpkg -i TrackerSetup.deb
Or with gDEBi,
prayag@prayag:~/Downloads$ sudo apt-get install gdebi
prayag@prayag:~/Downloads$ sudo gdebi TrackerSetup.deb
check about the installed package
prayag@prayag:~/Downloads$ dpkg -s gedit
http://askubuntu.com/a/17829/37643
chapter 11 => play popular non-free media formats (ubuntu)
sudo apt-get install ubuntu-restricted-extras
sudo apt-get install libavcodec-extra-53 libavcodec53 ffmpeg
References
How to install REALVNC gui in ubuntu 12.04?
How can I specify a display?
Installing & Running VNC on Redhat/RPM Linux
Starting firefox on a remote host (over ssh) opens a new window locally: what is happening?
visit url with command line
http://waxborg.servepics.com/opensuse/remote-administration/running-firefox-remotely-over-ssh
How to shut down the computer after a task has been completed?, http://askubuntu.com/a/15536
How can I install software or packages without Internet (offline)?
35 Tricky and Complex Unix Interview Questions and Commands (Part 1)
Linux Hacks gist, https://gist.github.com/prayagupd/4730009
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