Make a Better WORLD, If You Cannot to Do So, Make a Better YOU: January 2016

Thursday, January 28, 2016

analyzing and storing logs

Analyzing and storing logs:::

logfiles are maintained by rsyslog service::
/var/log directories contain a variety of log files:::

all the log configuration are stored in the /etc/rsyslog.conf

Log file rotation::
by logrotate utility : when rotated logfiles are renamed by with an extension indicating the date on which it was rotated:
/var/log/messages file becomes /var/log/messages-20150126
rotated on January 26 2015
(logrotate man page)

analyze a syslog entry::
[root@localhost ~]# tail -f /var/log/secure
Jan 27 19:34:25 localhost gdm-launch-environment]: pam_unix(gdm-launch-environment:session): session opened for user gdm by (uid=0)
Jan 27 19:34:37 localhost polkitd[947]: Registered Authentication Agent for unix-session:c1 (system bus name :1.30 [gnome-shell --mod

send a syslog message with logger::(confusion))

Reviewing systemd journal entries:::
journalctl command shows the full system journal starting with the oldest log entry.

[root@localhost ~]# journalctl
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Wed 2016-01-27 20:
Jan 27 19:33:21 localhost.localdomain systemd-journal[342]: Runtime jou
Jan 27 19:33:21 localhost.localdomain systemd-journal[342]: Runtime jou

By default journalctl gives last 10 log entries
specifying we can get our desired: for example to get the last 5 entries:
[root@localhost ~]# journalctl -n 5
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Wed 2016-01-27 20:
Jan 27 20:20:01 localhost.localdomain systemd[1]: Starting Session 8 of
Jan 27 20:20:01 localhost.localdomain CROND[5166]: (root) CMD (/usr/lib
Jan 27 20:30:01 localhost.localdomain systemd[1]: Started Session 9 of
Jan 27 20:30:01 localhost.localdomain systemd[1]: Starting Session 9 of
Jan 27 20:30:01 localhost.localdomain CROND[5367]: (root) CMD (/usr/lib
lines 1-6/6 (END)

also to log entry only those who have priority as err or above::
[root@localhost ~]# journalctl -p err
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Wed 2016-01-27 20:
Jan 27 19:33:23 localhost.localdomain kernel: sd 2:0:0:0: [sda] Assumin
Jan 27 19:33:36 localhost.localdomain systemd-udevd[760]: unable to mov
Jan 27 19:33:37 localhost.localdomain kernel: piix4_smbus 0000:00:07.3:
Jan 27 19:34:23 localhost.localdomain dhclient[2084]: receive_packet fa
Jan 27 19:34:28 localhost.localdomain dhclient[2084]: send_packet: Netw
Jan 27 19:34:28 localhost.localdomain dhclient[2084]: dhclient.c:2407:
Jan 27 19:34:32 localhost.localdomain pulseaudio[2916]: [alsa-source-ES

journalctl -f itself can displsy last 10 lines of the journal and even can display updated one.(replacement of use of tail)
also we can use options like yesterday ,today tomorrow combined with either --since or --until

root@localhost ~]# journalctl --since yesterday
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Wed 2016-01-27 20:
Jan 27 19:33:21 localhost.localdomain systemd-journal[342]: Runtime jou
Jan 27 19:33:21 localhost.localdomain systemd-journal[342]: Runtime jou
Jan 27 19:33:21 localhost.localdomain kernel: Initializing

also we can use date in YYYY-MM-DD format and time in HH-MM-SS format
[root@localhost ~]# journalctl --since 2015-12-23
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Wed 2016-01-27 20:
Jan 27 19:33:21 localhost.localdomain systemd-journal[342]: Runtime jou
Jan 27 19:33:21 localhost.localdomain systemd-journal[342]: Runtime jou
Jan 27 19:33:21 localhost.localdomain kernel: Initial

output the journal entries from 10 the february 2015 20:30:00 to 13th february 2015 12:00:00

[root@localhost ~]# journalctl --since "2015-02-10 20:30:00" --until "2015-02-13 12:00:00"

also we can view detail By::

[root@localhost ~]# journalctl -o verbose
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Wed 2016-01-27 20:
Wed 2016-01-27 19:33:21.697010 EST [s=d58dea757c3947e38eafaf5e1317364a;
PRIORITY=6
_TRANSPORT=driver
MESSAGE=Runtime journal is using 8.0M (max allowed 91.2M, trying to
MESSAGE_ID=ec387f577b844b8fa948f33cad9a75e6
_PID=342
_UID=0
_GID=0
_COMM=systemd-journal

Moreover we can access the particular process or event by using the options like::
_COMM the name of the command
_EXE the path to the execuatable for the process
_PID the PID of the process
_SYSTEM_UNIT the system unit that started the process.
can also be used combinely or individually such option::

[root@localhost ~]# journalctl _SYSTEM_UNIT=sshd.service _PID=112

journalctl with priority warning::
[root@localhost ~]# journalctl -p warning
-- Logs begin at Wed 2016-01-27 19:33:21 EST, end at Thu 2016-01-28 00:
Jan 27 19:33:21 localhost.localdomain kernel: ACPI: RSDP 00000000000f6a
Jan 27 19:33:21 localhost.localdomain kernel: ACPI: XSDT 000000007feea6
Jan 27 19:33:21 localhost.localdomain kernel: ACPI: FACP 000000007fefee
Jan 27 19:33:21 localhost.localdomain kernel: ACPI: DSDT 000000007feec0

Preserving the systemd journal::

store the journal permanently:

[root@localhost ~]# mkdir /var/log/journals
first of all a directory /var/log/journals is created.

[root@localhost ~]# chown root:systemd-journal /var/log/journals
change the ownership to root user and systemd-journal group for the file .

[root@localhost ~]# chmod 2755 /var/log/journals
then set the sticky bit so that every one can read and access but cannot delete the content.

[root@localhost ~]# kilall -USR1 systemd-journald
finally send the special USR1 signal as user root.

maintaining accurate time:::
timdatectl command
[root@localhost ~]# timedatectl
Local time: Thu 2016-01-28 13:06:07 EST
Universal time: Thu 2016-01-28 18:06:07 UTC
RTC time: Thu 2016-01-28 18:06:07
Time zone: America/New_York (EST, -0500)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no
DST active: no
Last DST change: DST ended at
Sun 2015-11-01 01:59:59 EDT
Sun 2015-11-01 01:00:00 EST
Next DST change: DST begins (the clock jumps one hour forward) at
Sun 2016-03-13 01:59:59 EST
Sun 2016-03-13 03:00:00 EDT

[root@localhost ~]# timedatectl list-timezones
Africa/Abidjan
Africa/Accra
Africa/Addis_Ababa
Africa/Algiers
Africa/Asmara

tzselect command is useful for identifying various timezones on the basis of countries or continents.
[root@localhost ~]# tzselect
Please identify a location so that time zone rules can be set correctly.
Please select a continent or ocean.
1) Africa
2) Americas
3) Antarctica
4) Arctic Ocean
5) Asia
6) Atlantic Ocean
7) Australia
8) Europe
9) Indian Ocean
10) Pacific Ocean

[root@localhost ~]# timedatectl set-time 9:00:00
Failed to set time: Automatic time synchronization is enabled

to set the current date[root@localhost ~]# timedatectl set-ntp false
to disable the network provided time.
Now we can change the time settings
[root@localhost ~]# timedatectl set-time 9:00:00
[root@localhost ~]# timedatectl
Local time: Thu 2016-01-28 09:00:06 MST
Universal time: Thu 2016-01-28 16:00:06 UTC
RTC time: Thu 2016-01-28 16:00:07
Time zone: America/Phoenix (MST, -0700)
root@localhost ~]# timedatectl set-time 1:45:00
[root@localhost ~]# timedatectl
Local time: Thu 2016-01-28 01:45:03 MST
Universal time: Thu 2016-01-28 08:45:03 UTC
RTC time: Thu 2016-01-28 08:45:04
Time zone: America/Phoenix (MST, -0700)
NTP enabled: no
NTP synchronized: no
RTC in local TZ: no
DST active: n/a
[root@localhost ~]# timedatectl set-ntp True
[root@localhost ~]# timedatectl
Local time: Thu 2016-01-28 11:46:24 MST
Universal time: Thu 2016-01-28 18:46:24 UTC
RTC time: Thu 2016-01-28 08:45:34
Time zone: America/Phoenix (MST, -0700)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no

[root@localhost ~]# timedatectl set-ntp True
[root@localhost ~]# timedatectl
Local time: Thu 2016-01-28 11:46:24 MST
Universal time: Thu 2016-01-28 18:46:24 UTC
RTC time: Thu 2016-01-28 08:45:34
Time zone: America/Phoenix (MST, -0700)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no
DST active: n/a

NTP enabled: no
Now agai we can change the time and enable the NTP

NTP synchronized: no
RTC in local TZ: no
DST active: n/a

configuring and monitoring chronyd((confusion)) time source change garney esko kaam chaai.....

for that we need to vi the given file first
[root@localhost ~]# vi /etc/chrony.conf
then change all the servers entries with the ip address of ur Pc as follows:

#use public servers fromthe pool.ntp.org project:::
server 192.168.122.1 iburst

Then restart the chronyd using systemctl command:

[root@localhost ~]# systemctl restart chronyd
now finally we can verify if the modifications is done ::
[root@localhost ~]# chronyc sources -v
210 Number of sources = 2

.-- Source mode '^' = server, '=' = peer, '#' = local clock.
/ .- Source state '*' = current synced, '+' = combined , '-' = not combined,
| / '?' = unreachable, 'x' = time may be in error, '~' = time too variable.
|| .- xxxx [ yyyy ] +/- zzzz
|| Reachability register (octal) -. | xxxx = adjusted offset,
|| Log2(Polling interval) --. | | yyyy = measured offset,
|| \ | | zzzz = estimated error.
|| | | \
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
^? 192.168.122.1 0 7 0 10y +0ns[ +0ns] +/- 0ns
^* ec2-52-0-56-137.compute-1 2 6 17 6 -1851us[-1279us] +/- 60ms

###confusion related to adding directive through echo command and logger commadn
for example::[root@localhost ~]# echo "authpriv.alert /var/log/auth-errors" > /etc/rsylog.d/auth-errors.conf

Thursday, January 21, 2016

RHL7 Configuring and securing openssh service::

Configuring and securing openssh service::

to connect to a remotehost as the current user:::
ssh 192.168.122.1

[root@localhost ~]# ssh 192.168.122.1(here current user is root,so we are logging as root in the remote host as well)
The authenticity of host '192.168.122.1 (192.168.122.1)' can't be established.
ECDSA key fingerprint is a1:48:e8:2b:14:09:43:19:be:44:31:eb:0a:65:7e:c8.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.122.1' (ECDSA) to the list of known hosts.
root@192.168.122.1's password:
Last login: Thu Jan 21 11:02:35 2016

connect to a remote shell as a different user.. Now i am root here and i want to connect as ashok in the remotehsot, then:
ssh ashok@remotehost
[root@localhost ~]# ssh ashok@192.168.122.1
ashok@192.168.122.1's password:
Last login: Thu Jan 21 14:31:50 2016 from 192.168.122.1

displaying and changing the hostname of remotehost
::::

[ashok@localhost ~]$ ssh ashok@192.168.122.1 hostname
ashok@192.168.122.1's password:
localhost.localdomain
[ashok@localhost ~]$ hostname ashok
hostname: you must be root to change the host name
[ashok@localhost ~]$ su -
Password:
Last login: Thu Jan 21 14:28:01 EST 2016 from 192.168.122.1 on pts/4
[root@localhost ~]# hostname remoteuser
[root@localhost ~]# hostname
remoteuser
[root@localhost ~]# su ashok
[ashok@remoteuser root]$ cd
[ashok@remoteuser ~]$ exit
exit
[root@localhost ~]# ssh ashok@192.168.122.1
ashok@192.168.122.1's password:
Last login: Thu Jan 21 14:39:44 2016
[ashok@remoteuser ~]$

SSH hostkeys:::

first time a user uses ssh to connect to particuylar server, it stores a public key in the users ~/.ssh/known_hosts and durig each logging
it checks for that match of public key and only then allows the connection;

COnfiguring ssh key_based authentication::
to connect to the remotehost, as we discussed earlier we need to match the public key however there is the secured way but we dont need to type password to conect to the remotehost:
for that we need to use following commands::(this is called public key authentication)

first of all
[ashok@localhost ~]$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/ashok/.ssh/id_rsa):
/home/ashok/.ssh/id_rsa already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/ashok/.ssh/id_rsa.
Your public key has been saved in /home/ashok/.ssh/id_rsa.pub.
The key fingerprint is:
12:8e:eb:23:bd:7c:26:18:58:d9:4e:db:35:19:d1:c6 ashok@remoteuser
The key's randomart image is:
+--[ RSA 2048]----+
| .+ |
| . E |
| o . + |
| o oo .+ |
| o o.oo.S. |
|. . o... |
| +. |
| oo+ o |
| .+* |
+-----------------+
[ashok@localhost ~]$ ssh-copy-id ashok@192.168.122.1
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
ashok@192.168.122.1's password:

Number of key(s) added: 1

Now try logging into the machine, with: "ssh 'ashok@192.168.122.1'"
and check to make sure that only the key(s) you wanted were added.

[ashok@localhost ~]$ ssh ashok@192.168.122.1
Last login: Thu Jan 21 16:10:14 2016( notice over here previously it used to ask for password but now it hasnot)
this is wha we can do with ssh key-gen to login to any remotehost that we have acces to

Costumizing ssh service configuration:::
resrticting ssh logins::
first of we have to generate ssh keys on remotehost;

[ashok@localhost ~]$ ssh key-gen
after completing the middle steps of this command we need
ssh-copy-id remotehost( this will copy id to the remotehost)

[ashok@localhost ~]$ ssh-copy-id 192.168.122.1

after some steps of the above command try logging into the remotehost

[ashok@localhost ~]$ ssh ashok@192.168.122.1
Last login: Thu Jan 21 16:40:17 2016 from 192.168.122.1
after logging in gain the root priviliges:;

[ashok@remoteuser ~]$ su -
Password:
Last login: Thu Jan 21 16:34:35 EST 2016 on pts/1
[root@remoteuser ~]#
now configure ssh on remoteuser to prevent root logins::

[root@remoteuser ~]# vi /etc/ssh/sshd_config
permitrootlogin no

[root@remoteuser ~]# systemctl restart sshd

again to prevent passwordauthentication

root@remoteuser ~]$ vi /etc/ssh/sshd_config
PasswordAuthentication no

[root@remoteuser ~
]# systemctl restart sshd
now again try connecting as root to remotehost, thi type it denied without asking for password
however last time it asked for password( now it didnt because we added passwordauthentication no) in /etc/ssh/sshd_config..

Controlling services and DAEMONS::

for the kernel representation of system CPUs

[root@localhost ~]# grep "model name" /proc/cpuinfo

model name : Pentium(R) Dual-Core CPU E5300 @ 2.60GHz

Controlling services and DAEMONS::

daemons are processes that wait or run in the background performing various tasks.

To view the status of a service::

systemctl status name.type

without type it will display the status of a service unit, if one exists

root@localhost ~]# systemctl status sshd.service

● sshd.service - OpenSSH server daemon

Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)

Active: active (running) since Thu 2016-01-21 09:47:09 EST; 3h 22min ago

Docs: man:sshd(8)

man:sshd_config(5)

Main PID: 1535 (sshd)

CGroup: /system.slice/sshd.service

└─1535 /usr/sbin/sshd -D

Jan 21 09:47:09 localhost.localdomain systemd[1]: Started OpenSSH serve...

Jan 21 09:47:09 localhost.localdomain systemd[1]: Starting OpenSSH serv...

Jan 21 09:47:10 localhost.localdomain sshd[1535]: Server listening on 0...

Jan 21 09:47:10 localhost.localdomain sshd[1535]: Server listening on :...

Jan 21 09:59:42 localhost.localdomain sshd[4268]: Accepted password for...

Jan 21 11:01:34 localhost.localdomain sshd[6101]: Accepted password for...

Jan 21 12:22:57 localhost.localdomain sshd[8134]: Accepted password for...

Hint: Some lines were ellipsized, use -l to show in full.

to query the state of only service units::

systemctl --type=service

to view if there are any failed or maintainence state::

systemctl status rngd.service -l ( -l option will show the long listing)

alternate commands to check whether the particular command is active or not...

root@localhost ~]# systemctl is-active sshd( it shows whether its current state is active or not)

active

[root@localhost ~]# systemctl is-enabled sshd (it shows whether it was enabled at boot time or not)

enabled

to list all active state of all loaded units::

systemctl list-units --type=service

[root@localhost ~]# systemctl list-units --type=service

UNIT LOAD ACTIVE SUB DESCRIPTION

abrt-ccpp.service loaded active exited Install ABRT coredump ho

abrt-oops.service loaded active running ABRT kernel log watcher

abrt-xorg.service loaded active running ABRT Xorg log watcher

abrtd.service loaded active running ABRT Automated Bug Repor

accounts-daemon.service loaded active running Accounts Service

alsa-state.service loaded active running Manage Sound Card State

atd.service loaded active running Job spooling tools

auditd.service loaded active running Security Auditing Servic

avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack

blk-availability.service loaded active exited Availability of block de

bluetooth.service loaded active running Bluetooth service

if -all option is used (systemctl list-units --type=service --all) it even displays inactive units

TO list all socket units active or inactive in the system::

systemctl list-units --type=socket --all

To display if sshd is active without displaying all other status information::

systemctl is-active sshd

[root@localhost ~]# systemctl is-enabled sshd

enabled

Now if we have to display even other status information::

systemctl status sshd

List the enabled and disabled states of all service units::

systemctl list-units --type=service --all

Unit dependcies::

services may have depencies on one another. For example if we have to stop printing services , we have to stop

all three units related to that very unit that may be from other units

masking services::

if there are conflicting services installed and we dont want to open up tha conflicted service accidently we have to mask that

service to /dev/null.

systemctl mask network

[root@localhost ~]# systemctl mask network

Created symlink from /etc/systemd/system/network.service to /dev/null.

Now the service cannot be opened manually as well as automatically

restarting a service will change its process id..

but reloading wont change any process id and no connections are interrupted

enabling any service will make it ready to start at system boot

Processes:::
parent process
child process
different process states::
R = task running
S = sleeping
D = sleeping (but interruptible)
K =task killable
T = task stopped
Z=exit zombie(a child process signals as its parents exits
.all resources except for the process identity (PID) are realeased
X= exit dead

listing processes:: ps -aux ( displays all processes with columns in which users will be
interested)

[ashok@localhost ~]$ ps -aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.3 0.3 126588 7384 ? Ss 09:46 0:04 /usr/lib/syste
root 2 0.0 0.0 0 0 ? S 09:46 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? S 09:46 0:00 [ksoftirqd/0]
root 5 0.0 0.0 0 0 ? S< 09:46 0:00 [kworker/0:0H]
root 6 0.0 0.0 0 0 ? S 09:46 0:00 [kworker/u256:
root 7 0.0 0.0 0 0 ? S 09:46 0:00 [migration/0]
root 8 0.0 0.0 0 0 ? S 09:46 0:00 [rcu_bh]
root 9 0.0 0.0 0 0 ? S 09:46 0:00 [rcuob/0]
root 10 0.0 0.0 0 0 ? S 09:46 0:00 [rcuob/1]
root 11 0.0 0.0 0 0 ? S 09:46 0:00 [rcuob/2]
root 12 0.0 0.0 0 0 ? S 09:46 0:00 [rcuob/3]
root 13 0.0 0.0 0 0 ? S 09:46 0:00 [rcuob/4]

ps -lax gives more technical detail and more faster coz it doesnt
provide username( ps -ef is also a unix command to look all processes)

[ashok@localhost ~]$ ps -lax
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
4 0 1 0 20 0 126588 7384 ep_pol Ss ? 0:04 /usr/lib/
1 0 2 0 20 0 0 0 kthrea S ? 0:00 [kthreadd
1 0 3 2 20 0 0 0 smpboo S ? 0:00 [ksoftirq
1 0 6 2 20 0 0 0 worker S ?

0:00 [kwo

Controlling jobs::
running jobs in the background::

[ashok@localhost ~]$ sleep 1000 &
[1] 4998
checking if jobs is running:
[ashok@localhost ~]$ jobs
[1]+ Running sleep 1000 &

bringing job in the foreground:;
[ashok@localhost ~]$ fg %1
sleep 1000

To again send the job to background and send the suspend request
press Ctrl-z
[ashok@localhost ~]$ fg %1
sleep 1000
^Z
[1]+ Stopped sleep 1000

ps with option j displays job information including the command shell of each session
ashok@localhost ~]$ ps j
PPID PID PGID SID TTY TPGID STAT UID TIME COMMAND
4146 4150 4150 4150 pts/0 4150 Ss+ 1000 0:00 /bin/bash
4272 4274 4274 4274 pts/1 5174 Ss 1000 0:00 -bash
4274 5165 5165 4274 pts/1 5174 T 1000 0:00 sleep 1000
4274 5174 5174 4274 pts/1 5174 R+ 1000 0:00ps j

Killing processes::
to list signals

[ashok@localhost ~]$ kill -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX

we can use killall to send signal for more processes at once under
certain pattern.
even pkill is used to send signal to multiple processes at once
pkill command_pattern
pkill -signal command_pattern
pkill -G GID command_pattern
pkill -t terminal_name -U UID command_pattern

pgrep -l -u username searches for all the processes associated with that username

[root@localhost ~]# pgrep -l -u ashok
3280 gnome-keyring-d
3323 gnome-session
3330 dbus-launch
3331 dbus-daemon
3396 gvfsd
3400 gvfsd-fuse
3475 ssh-agent
3491 at-spi-bus-laun
3495 dbus-daemon
3500 at-spi2-registr
3511 gnome-settin

To see all the process tree for the system or single user, we use pstree command
[root@localhost ~]# pstree -p ashok

at-spi-bus-laun(3491)─┬─dbus-daemon(3495)───{dbus-daemon}(3497)
├─{at-spi-bus-laun}(3492)
├─{at-spi-bus-laun}(3494)
└─{at-spi-bus-laun}(3496)
pkill -p 3491 will kill all the children they have created because
here the PPID is 3491 and parent is at-spi-bus-laun(3491)

Thursday, January 14, 2016

groupmod,usermod ,passwords(Red Hat 7)

groupmod uses:::
groupmod -n newmane oldname

to modify existing groupids
groupmod -g 2000 ateam( suppose previously roup a ateam has agroup id of 1005 now it will be 2000)

usermod even helps change a group of auser::
usermod -g newgroup username
(now it will assign the username to newgroup

adding a supplemental group to a user

usermod -aG newgroup username
(this will append a newgroup that is supplemental one for the username)

differences between groupmod and groupadd ??
groupmod just changes the name and group id of a existing group whereas usermod can change the group of a existing group, append a supplemental group to any existing user..the examples can be seen above..

managing user passwords::
passwords stored in /etc/shadow file

three parts in amodern password
$1$gCj La2/Z$6 Pu0EK0AzfCj xj v2ho LOB/

1.. 1: The hashing algorithm .The number 1 indicates an MD5 hash. the number 6 appears when $HA-512 hash is used
2. gCjLa2/Z: The salt used to encrypt the hash.
3:6Pu0 EK0AzfCj x j v2ho LOB/: the encrypted hash

authconfig - - passalgo ::: a command that determines which is the appropriate setting for password protection in /etc/shadow file

Password aging::;
The several options are as follows::
chage -d 0 username ::: will force a user to update on next login..
chage -l username :: will list a username current settings

chage -E yyyy-mmmm-DD will expire an account on specific day
#nologin sheel (confusion)

Sunday, January 10, 2016

RHL7 adding users as sudoers

how to grant sudo privilege to new user names as 'mynewuser'

for that we need to carry out the following steps;

become root: su -
then type the command: visudo
search for the following #allow root to run any command anywhere
add the following by inserting:

mynewuser ALL=(ALL) ALL
save and quit:wq

installing vmware

how to install vmware on linux
first of download vmare bundle on ur pc inside Downloads and follow the following steps;;

ashok@ashok:~$ sudo apt-get install build-essential linux-headers-`uname -r`
Reading package lists... Done
Building dependency tree
Reading state information... Done
build-essential is already the newest version.
linux-headers-3.16.0-44-generic is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 4 not upgraded.

change your current directory to downloads and list all available over there

ashok@ashok:~$ cd /home/ashok/Downloads

ashok@ashok:~/Downloads$ ls -l
total 1642660
-rw-r----- 1 ashok ashok 241754 Oct 4 14:11 11696607_1596467153963786_4550855425001071167_o.jpg
-rw-r----- 1 ashok ashok 414803 Oct 4 14:10 11907155_1616732095270625_3006793256146796048_o.jpg
-rw-r----- 1 ashok ashok 59291 Nov 29 20:17 12311397_909014092528437_123997452_o.jpg
-rw-r----- 1 ashok ashok 57180 Oct 7 22:47 18373101441-459318804-registration.pdf
-rw-rw-r-- 1 ashok ashok 4852 Nov 5 10:42 1920330_1081231035228105_976989325251166712_n.jpg
-rw-rw-r-- 1 ashok ashok 8639 Nov 22 19:47 2(1).py
-rw-r----- 1 ashok ashok 55929 Sep 22 17:25 267549_108259742603880_7115829_n.jpg
-rw-rw-r-- 1 ashok ashok 8639 Nov 22 19:15 2.py
-rw-r----- 1 ashok ashok 38579 Sep 22 17:28 483511_357713057658546_777917237_n.jpg
-rw-r----- 1 ashok ashok 46951 Sep 22 17:26 560583_341516452611540_36203639_n.jpg
-rw------- 1 ashok ashok 136287 Sep 23 10:28 ACFrOgCca7kki9pxYYoWEC9tt4wb3yBsCYWQxgdvlWhfmRS9tVp9IwabFONpoziLEUK3blkFohOE2AlkyGpB2S8rrB-srsZj2K5AQLTnr3BdQj8YYRxh9M_KdHOmgpU=_print=true&nonce=pn31j11aabh4k&user=12749395014731097935&hash=hflelu3ego4dl7jak1n25q2p74p41113.pdf
-rw-r----- 1 ashok ashok 4368 Oct 25 10:15 adobe-release-i386-1.0-1.noarch.rpm
-rw-r----- 1 ashok ashok 155342 Jan 9 23:31 A Freshman's Guide to Tech Internships.pdf
-rw-r----- 1 ashok ashok 8029 Oct 13 22:28 AfricanStudiesSecondExamDefinition.docx
-rw-r----- 1 ashok ashok 135603 Oct 13 20:56 African-Studies-_-Second-Exam-Definition.pdf.docx
-rw-rw-r-- 1 ashok ashok 28820 Nov 17 10:37 article_clippings.zip
-rw-r----- 1 ashok ashok 13395 Sep 18 21:37 ashok essay.docx
-rw-rw-r-- 1 ashok ashok 6244 Dec 13 20:01 Ashok_hangman2(1).py
-rw-rw-r-- 1 ashok ashok 6244 Dec 13 20:02 Ashok_hangman2(2).py
-rw-rw-r-- 1 ashok ashok 6244 Dec 13 20:03 Ashok_hangman2(3).py
-rw-rw-r-- 1 ashok ashok 6244 Dec 13 19:58 Ashok_hangman2.py
-rw-rw-r-- 1 ashok ashok 1514 Nov 22 19:17 ashok.py
-rw-r----- 1 ashok ashok 18270 Nov 29 19:19 Ashok submission.docx
-rw-r----- 1 ashok ashok 666894336 Sep 24 20:46 CentOS-7-x86_64-Minimal-1503-01.iso
-rw-r----- 1 ashok ashok 0 Oct 21 21:52 computer science homework
-rw-r----- 1 ashok ashok 9409 Sep 23 22:07 CopyofDay10PracticeExamforSept29thTest.docx
-rw-r----- 1 ashok ashok 20565248 Jan 9 23:34 Day 01 lecture- What is CS-.pptx
-rw-r----- 1 ashok ashok 687650 Jan 9 23:34 Day 02 lecture- Programs, programming, and Python Slides.pptx
-rw-r----- 1 ashok ashok 37874 Oct 7 20:04 doc.pdf
-rw-r----- 1 ashok ashok 14814 Oct 5 21:52 EGPP CareerAssignment.docx
-rw-r----- 1 ashok ashok 86528 Sep 30 07:33 ENGW 104 Syllabus (Fall 2015) Section 7 (1).doc
-rw-r----- 1 ashok ashok 86528 Oct 6 22:45 ENGW 104 Syllabus (Fall 2015) Section 7 (2).doc
-rw-r----- 1 ashok ashok 86528 Oct 6 22:46 ENGW 104 Syllabus (Fall 2015) Section 7 (3).doc
-rw-r----- 1 ashok ashok 86528 Oct 6 22:51 ENGW 104 Syllabus (Fall 2015) Section 7 (4).doc
-rw-r----- 1 ashok ashok 86528 Oct 7 21:38 ENGW 104 Syllabus (Fall 2015) Section 7 (5).doc
-rw-r----- 1 ashok ashok 86528 Oct 7 21:47 ENGW 104 Syllabus (Fall 2015) Section 7 (6).doc
-rw-r----- 1 ashok ashok 86528 Oct 11 20:22 ENGW 104 Syllabus (Fall 2015) Section 7 (7).doc
-rw-r----- 1 ashok ashok 86528 Oct 25 12:12 ENGW 104 Syllabus (Fall 2015) Section 7 (8).doc
-rw-r----- 1 ashok ashok 86528 Oct 25 14:06 ENGW 104 Syllabus (Fall 2015) Section 7 (9).doc
-rw-r----- 1 ashok ashok 86528 Sep 30 07:33 ENGW 104 Syllabus (Fall 2015) Section 7.doc
-rw-r----- 1 ashok ashok 14615 Oct 12 14:28 Essay-10.docx
-rw-r----- 1 ashok ashok 14631 Oct 13 09:20 Essay-11 (1).docx
-rw-r----- 1 ashok ashok 14631 Oct 12 14:28 Essay-11.docx
-rw-r----- 1 ashok ashok 14207 Oct 13 09:20 Essay-12 (1).docx
-rw-r----- 1 ashok ashok 14207 Oct 12 14:28 Essay-12.docx
-rw-r----- 1 ashok ashok 14574 Oct 13 09:21 Essay-13 (1).docx
-rw-r----- 1 ashok ashok 14574 Oct 12 14:28 Essay-13.docx
-rw-r----- 1 ashok ashok 8736 Oct 13 00:40 Essay-14.docx
-rw-r----- 1 ashok ashok 13073 Sep 18 21:21 Essay #1.docx
-rw-r----- 1 ashok ashok 14990 Oct 12 09:37 Essay-1.docx
-rw-r----- 1 ashok ashok 14588 Oct 12 14:28 Essay-2 (1).docx
-rw-r----- 1 ashok ashok 14588 Oct 13 09:21 Essay-2 (2).docx
-rw-r----- 1 ashok ashok 14588 Oct 12 11:31 Essay-2.docx
-rw-r----- 1 ashok ashok 17545 Oct 12 14:28 Essay-3.docx
-rw-rw-r-- 1 ashok ashok 230126 Nov 16 10:04 essay 3 draft.docx
-rw-r----- 1 ashok ashok 15116 Oct 12 14:28 Essay-4.docx
-rw-r----- 1 ashok ashok 15026 Oct 12 14:28 Essay-5.docx
-rw-r----- 1 ashok ashok 15731 Oct 12 14:28 Essay-6.docx
-rw-r----- 1 ashok ashok 16403 Oct 12 14:28 Essay-7 (1).docx
-rw-r----- 1 ashok ashok 16403 Oct 12 14:28 Essay-7.docx
-rw-r----- 1 ashok ashok 14075 Oct 12 14:28 Essay-9.docx
-rw-rw-r-- 1 ashok ashok 9531 Nov 10 23:00 final resume.docx
-rw-rw-r-- 1 ashok ashok 6533 Nov 10 22:52 google essay.docx
-rw-rw-r-- 1 ashok ashok 13189 Dec 7 00:06 hangman2final.py
-rw-rw-r-- 1 ashok ashok 3004 Dec 6 21:42 hangman4.py
-rw-rw-r-- 1 ashok ashok 58003 Dec 5 19:52 hangman_english_words.txt
-rw-rw-r-- 1 ashok ashok 58003 Dec 5 19:52 hangman_english_words.txt~
drwxrwxr-x 4 ashok ashok 4096 Sep 5 19:41 install_flash_player_11_linux.x86_64
-rw-rw-r-- 1 ashok ashok 7266504 Sep 5 19:41 install_flash_player_11_linux.x86_64.tar.gz
-rw-r----- 1 ashok ashok 9911233 Oct 20 09:49 Learning_Python_-_Mark_Lutz (1).pdf
-rw-r----- 1 ashok ashok 5035772 Oct 20 08:44 Learning_Python_-_Mark_Lutz.epub
-rw-r----- 1 ashok ashok 9911233 Oct 20 08:44 Learning_Python_-_Mark_Lutz.pdf
drwxrwxr-x 3 ashok ashok 12288 Sep 12 13:07 mobile
-rw-rw-r-- 1 ashok ashok 6098 Dec 6 19:58 my project 2(1).py
-rw-rw-r-- 1 ashok ashok 5467 Dec 6 21:09 My project 2 of python.py
-rw-rw-r-- 1 ashok ashok 5468 Dec 6 21:09 My project 2 of python.py~
-rw-rw-r-- 1 ashok ashok 6098 Dec 6 19:46 my project 2.py
-rw-r----- 1 ashok ashok 70144 Sep 6 12:08 occ_15-1122.xls
-rw-r----- 1 ashok ashok 49366 Oct 7 20:28 out.pdf
-rw-r----- 1 ashok ashok 8924 Sep 17 10:18 paperratergffdhyh.docx
-rw-rw-r-- 1 ashok ashok 3132 Dec 6 23:05 part2.py
-rw-rw-r-- 1 ashok ashok 3187 Dec 5 15:39 project 1 cs(1).py
-rw-rw-r-- 1 ashok ashok 3187 Dec 13 19:59 project 1 cs(2).py
-rw-rw-r-- 1 ashok ashok 3187 Nov 22 22:12 project 1 cs.py
-rw-r----- 1 ashok ashok 1948323 Jan 9 19:50 putty-0.66 (1).tar.gz
-rw-r----- 1 ashok ashok 1948323 Jan 9 19:50 putty-0.66.tar.gz
-rw-r----- 1 ashok ashok 524288 Jan 9 22:22 putty.exe
-rw-r----- 1 ashok ashok 16168 Oct 6 08:55 Resume.docx
-rw-r----- 1 ashok ashok 7865872 Jan 9 22:35 RH134-RHEL7(1) (1).pdf
-rw-r----- 1 ashok ashok 7865872 Jan 9 19:20 RH134-RHEL7(1).pdf
-rw-r----- 1 ashok ashok 5438245 Sep 5 17:27 Shell Programming in 24 Hours.pdf
-rw-r----- 1 ashok ashok 178159 Sep 21 08:35 Solutions to 156 sample Test 1 Fall 2015 Correct File.pdf
-rw-rw-r-- 1 ashok ashok 32164 Sep 5 19:47 Supp Syll 2015.docx
-rw-r----- 1 ashok ashok 221594545 Sep 5 20:54 The Seagull Handbook, 2nd Edition.pdf
-rw-r----- 1 ashok ashok 1193988 Sep 5 20:51 The Word_ Black Writers Talk Ab - Marita Golden.pdf
-rw-rw-r-- 1 ashok ashok 5481 Sep 6 16:01 Untitled 1.docx
-rw-r----- 1 ashok ashok 63279710 Sep 24 20:18 virtualbox-5.0_5.0.4-102546-Ubuntu-trusty_amd64.deb
-rw-r----- 1 ashok ashok 138848126 Jan 10 11:41 VMware-Player-12.1.0-3272444.x86_64 (1).bundle
-rw-r----- 1 ashok ashok 138848126 Jan 10 00:43 VMware-Player-12.1.0-3272444.x86_64.bundle

select the one which we have to install and follow the following command:;

ashok@ashok:~/Downloads$ gksudo bash ./VMware-Player-12.1.0-3272444.x86_64.bundle

this helps you to get the graphical interface and one can follow their step to carry out the installation process;

Thursday, January 7, 2016

history to practice for RHEL7 book 2(personal)

812 date
813 grep '^Jan *4 2[123]' /root
814 grep '^Jan *4 2[123]' door.log
815 pwd
816 grep '^Jan *4 2[123]' door.log
817 grep ^door
818 mkdir logsss
819 cp door.log logsss
820 ls -lr logsss
821 date
822 grep '^Jan *4 2[234]*' /logsss/door.log
823 which door.log
824 cd logsss
825 pwd
826 grep '^Jan *4 2[234]*' /root/logsss/door.log
827 $!
828 $?
829 cd
830 man grep
831 cat >>ashok123
832 date
833 ls -l | grep -i '* jan 4 23:*"
834 ls -l | grep -i '* jan 4 23:*'
835 ls -l
836 ls -l | grep -i '* jan 4 23:13*' ashok123
837 ls -l | grep -i '* jan 4 23:13*' ashok123 |cat
838 vim /etc/hosts
839 cd
840 exit
841 vim /etc/mod
842 vim /etc/motd
843 ssh ashok@localhost
844 ssh localhost
845 ssh ashok@localhost
846 vim /etc/motd
847 ssh ashok@localhost
848 vim /etc/motl
849 vim /etc/motd
850 ssh ashok@localhost
851 ping 192.168.10.110
852 cat usr/shr/share/doc/ sos-3.2
853 cd usr/shr/share
854 cd /usr
855 ls -l
856 cd local
857 ls -l
858 cd share
859 ls
860 ls -l
861 su ashok
862 yum install python
863 fdisk -l
864 fdisk /dev/sdb
865 df -h
866 blkid /dev/sdb1
867 mount UUID="1f25b100-13bc-4f91-957a-4eea740bc9f1" /mnt
868 cd/mnt
869 cd /mnt
870 ls
871 mkdir practice
872 ls
873 touch i am practicing hard
874 ls -ltr
875 pwd
876 cd /
877 df -h /mnt
878 unmount /mnt
879 umount /mnt
880 df -h /mnt
881 cd /mnt
882 ls
883 ls -l
884 cd
885 mount /dev/mnt/sdb1 /mnt
886 cd /mnt
887 ls -l
888 blkid /dev/mnt/sdb1 /mnt
889 blkid /dev/sdb1 /mnt
890 mount /dev/sdb1 /mnt
891 cd mount
892 cd /mnt
893 ls -l
894 fdisk
895 umount /dev/sdb1
896 cd
897 umount /dev/sdb1
898 blkid /dev/sdb2
899 atq
900 at -l
901 at -c
902 mkdir home/my job
903 mkdir home/myjob
904 mkdir /home/myfile
905 echo "date > /home/myfile | at now +3min
906 echo "date > /home/myfile" | at now +3min
907 atq
908 at -c 1
909 atq
910 while [$atq | wc -l ) -gt 0];do sleep 1; done
911 echo 'date > /home/myfile' | at now +3min
912 while [$(atq | wc -l) -gt 0];do sleep 1; done
913 while [$(atq | wc -l) -gt 0]; do sleep 1; done
914 while [ $(atq | wc -l) -gt 0 ]; do sleep 1; done
915 cat myfile
916 pwd
917 ls -ltr
918 more anaconda-ks.cfg
919 mount 192.168.10.110:/home/users /mnt
920 ping 192.168.10.110
921 touch best.$$
922 ld -ltr
923 ls -ltr
924 echo "date > /var/tmp/myjob.txt" | at now +3min
925 atq
926 date
927 ls -l /var/tmp/myjob.txt
928 date
929 atq
930 atq | wc -l
931 date
932 at 19.45 echo hello
933 at 19:45
934 atq
935 date
936 at 19:45
937 date
938 at 19:48
939 ls -l /var/tmp/myfile.2
940 atq
941 date
942 ls -l /var/tmp/myfile.2
943 crontab -eu ashok
944 crontab -lu ashok
945 ls -l /var/tmp/myhello.txxt
946 date
947 crontab -eu ashok
948 ls -l /var/tmp/myhello.txxt
949 crontab -lu ashok
950 date
951 ls -l /var/tmp/myhello.txxt
952 crontab -lu ashok
953 ls -l /var/tmp/myhello.txxt
954 more /var/tmp/myhello.txxt
955 crontab -lu ashok
956 su - ashok
957 more /etc/cron.d/sysstat
958 sar
959 df -h
960 tmpwatch
961 yum search tmpwatch
962 ls -l /etc/*release*
963 more /etc/os-release
964 yum clean all
965 ls -l /usr/lib/tmpfiles.d/*.conf
966 more /usr/lib/tmpfiles.d/tmp.conf
967 systemd-tmpfiles
968 man 5 tmpfiles
969 man tmpfiles
970 yum search tmpfiles.
971 man tmpfiles.d
972 ps -ef | more
973 top
974 df -h
975 ps -ef| more
976 man ps
977 ps -ef |more
978 ps axo pid,comm,nice,time --sort=nice
979 ps axo pid,comm,nice,time --sort=nice | more
980 ps axo pid,comm,nice,time,cls --sort=nice | more
981 pwd
982 time du -sh *
983 nice -n 15 time du -sh *
984 nice -n 15 firefox
985 top
986 su - ashok
987 ps -ef| grep 18729
988 top
989 ps axo pid,comm,nice --sort=nice
990 ps axo pid,comm,nice --sort=nice | grep 18729
991 renice -n -15 18729
992 ps axo pid,comm,nice --sort=nice | grep 18729
993 cat /proc/cpuinfo | grep -i processor
994 grep -c '^processor' /proc/cpuinfo
995 grep -i processor /proc/cpuinfo
996 cd /home/ashok/lab2
997 ls -l
998 getfacl bestfile
999 su - ashok
1000 su - kamal
1001 yum install cifs-utils sambaclient
1002* yum install -y smb-client
1003 yum install -ysamba-client
1004 yum install -y samba-client
1005 smbclient -L //192.168.10.2
1006 mount -t cifs -u ashok //192.168.10.2/Users/suvi/Desktop/ashok /mnt
1007 mount -t cifs -o ashok //192.168.10.2/Users/suvi/Desktop/ashok /mnt
1008 mount -t cifs //192.168.10.2/Users/suvi/Desktop/ashok /mnt
1009 df -h /mnt
1010 cd /mnt
1011 ls
1012 mkdir test
1013 mkdir best
1014 touch creating files here
1015 mkdir /cifsshare
1016 mount -t cifs -o username=ashok //192.168.10.2/Users/suvi/Desktop/ashok /cifsshare
1017 ls -ld /cifsshare
1018 su - ashok
1019 chmod g+w /cifsshare
1020 su - ashok
1021 chmod o+w /cifsshare
1022 su - ashok
1023 mount -o remount /cifsshare/
1024 su - ashok
1025 chmod -R 775 /cifsshare/
1026 ls -ld /cifsshare/
1027 history
[root@private mnt]#

Wednesday, January 6, 2016

A python list interview question

interview preparation questions:::

def extendlist(val,list=[]):
list.append(val)
return list
list1 = extendlist(10)
list2 = extendlist(123,[])
list3 = extendlist('a')
print "list1 = %s" % list1
print 'list2 = %s" % list2
print "list3 = %s' % lsit3

hint prepared by myself::;
%s means a place holder that formats values into strings; for example::
name =raw_input("who are you?")
print " hello %s" % (name)
here %s tokens allows to insert and ( potentially format) a string.Notice that the %s token is replace by whatever i pass to the string after % symbol.
"Hello %s, my name is %s" % ('john', 'mike') # Hello john, my name is mike".
for integer %d is used instead of %s.

the output fort this question is
list1 = [10,'a']
list2 = [123]
list3 = [10,'a']
the output may not be the one we used to get on regular way but it is quite different because the argument is not set to default value of [] each time extendlist is called
however what actually happens is that the new default list is created
only once when the function is defined and the that same list is then then used subsquently whenever extendlist is invoked without a list argument being specified. This is because expressions in default arguments are calculated when the functions is defined ,not when it's called.
source:http://www.toptal.com/python/interview-questions

Tuesday, January 5, 2016

yum repo

[root@ashok yum.repos.d]# cat /tmp/a | awk '{$1=""; print $0}'
rpm -ivh httpd-2.4.6-40.el7.centos.x86_64.rpm
rpm -ih httpd-2.4.6-40.el7.centos.x86_64.rpm
rpm -i httpd-2.4.6-40.el7.centos.x86_64.rpm
ls -l bind*
rpm -ivh bind-9.9.4-29.el7.x86_64.rpm
rpm -ivh bind-libs-9.9.4-29.el7.x86_64.rpm
yum search bind
yum clean all
yum repolist
pwd
cd /etc/yum.repos.d/
ls
cat CentOS-CR.repo CentOS-fasttrack.repo CentOS-Sources.repo kern.repo
clear
ls
vi kern.repo
yum repolist
yum search bind
ls
mv CentOS-CR.repo CentOS-fasttrack.repo CentOS-Sources.repo kern.repo
mv kern.repo kern.repo.oldie
yum repolist
yum search bind
yum search bind | more
yum search bind.x86_64
yum install bind
pwd
cd -
ls -l httpd-tools-2.4.6-40.el7.centos.x86_64.rpm
more /boot/grub2/grub.cfg
ls -l /etc/grub2.cfg
more ../boot/grub2/grub.cfg
more /boot/grub2/grub.cfg
more /etc/yum.conf
pwd
ls
cd -
ls
more CentOS-Base.repo
yum repolist
yum list yum*
yum list httpd
yum list bind
yum list installed
yum list installed | wc -l
yum grouplist
yum list 'http*'
yum list 'http'
yum list http
yum list httpd
yum search all 'web server'
yum info httpd
yum provides /var/named
yum provides /var/www/html/
yum update httpd
yum list kernel
uname -r
uname -a
yum group list
yum group info "identiry management server"
yum group info "identiry Management Server"
yum group info "identity Management Server"
yum group install "Infiniband support"
yum history
history
yum.repos.d]#

big o notation python

def print_all_numbers_then_all_pair_sums(list_of_numbers):

print "these are the numbers:"
for number in list_of_numbers: #here n is the big o notation
print number

print "and these are their sums:"
for first_number in list_of_numbers: # here n^2 is the big o notation
for second_number in list_of_numbers:
print first_number + second_number

#Here our runtime is O(n + n^2) which we call O(n^2).Even if it was O(n^2 + 100n), it would still be O(n^2).

talking about worst case:
source :://www.interviewcake.com/article/python/big-o-notation-time-and-space-complexity
def contains(haystack,needle):
#does the haystack contain the needle?
for item in haystacK:
if item==needle:
return True
return False
here we might have 100 items in our haystack , but the first item might be the needle , in which case we would return in just 1 iteration of our loop
in general way we'd say this is O(n) runtime and the worst case parrt would be implied.But to be more specific we could say this is worst case O(n) and the best case O(1) rutime. For some algorithms we can also make rigorous statements about the "average case" runtime

space complexity: the final frontier:
sometimes we want to optimize for using less memory instead of ( or in addition) using less time.Talking about the memory cost ( or "space complexity") is very similiar to talking about time cost. We simply look at the total size ( relative to the size of the input) of any new variables we are allocating
the function takes 0(1) space ( we aren't allocating any new variable)

def say_hi_n_times(n):
for time in range(n):
print "hi"

the function takes O(n) space(the size of hi_list scales with the size of the input):

now the following function takes O(n) space ( the size of the hi_list scales with the size of the input):
def list_of_hi_n_times(n):
hi_list=[]

for time in range(n):
hi.list.append('hi')
return hi_list
usually when we talk about space complexity we are talking about additional space:

we dont include space taken up by the inputs.For eg: this function takes constant space even though the input has n items:

def get_largest_item(list_of_items):
largest=0
for item i list_of_items:
if item > largest:
return largest

Big O anaylis is awesome except when it is not

You should make a habit of thinking about the time and space complexibility of algorithms as you design them. Before long this'll become second nature ,allowing you to see optimizations and potential performances issues right away

source :://www.interviewcake.com/article/python/big-o-notation-time-and-space-complexity

Monday, January 4, 2016

VIM EDITOR RHEL7

editing in vi

from command mode to insert mode::
i = switch to insert mode and start inserting before the current position

a = switch to insert mode and start inserting afer the current position
A =move the cursor end of the current line switch to insert mode
I = switch to the end of the line nd also inser mode
O= open a new line above the current one and switch to insert mode
o = open a new line below the current one and switch to insert mode

h = cursor left one position
l = cursor right one position
j =cursor one down position
k = cursor one line up
^ = move to the beginning of the current line
$ = move to the end of the current line
gg = move to the first line of the document
G = move to the last line of the document
w = move cursor to the beginning of next word ( incudes punctuation)
W= move cursor to the beginning of next word( escapes punctuation)
b= move cursor to the beginning of previous word ( includes punctuation)
B = move cursor to the beginning of previous word ( doesnt include punctuation as a word)
( = move cursor to the beginning of previous/current sentence
) = move cursor to the beginning of next sentence
{ = move cursor to the beginning of current/previous paragraph
} = move cursor to the beginning of the next paragraph
x = to delete the character where cursor is placed
X = to delete the one character ahead of cursor
R = to replace the entire word
r = just to replace a single character
cw = to change from the current cursor position to the end of the file
cc = replace the entire line ( multiples lines if prefixed with the number)

rhel 7 grep command use

`[ashok@private ~]$ cat >dogs
cat
dog
concatenate
dogma
category
educated
[ashok@private ~]$ greo -i cat
bash: greo: command not found...
[ashok@private ~]$ grep -i cat
[ashok@private ~]$ grep -i 'cat'
^C
[ashok@private ~]$ grep -i 'cat' dogs
cat
concatenate
category
educated
[ashok@private ~]$ grep -iv cat dogs
dog
dogma
[ashok@private ~]$ grep -v ^[#] dogs
cat
dog
concatenate
dogma
category
educated
[ashok@private ~]$ grep -e 'cat' -e
]grep: option requires an argument -- 'e'
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.
[ashok@private ~]$ grep -e 'cat' -e 'dogs' dogs
cat
concatenate
category
educated
[ashok@private ~]$

Sunday, January 3, 2016

RHEL 7 networking examples

1. List all available interface on the system

[root@ashok ~]# nmcli connection show
- only to show active ones
[root@ashok ~]# nmcli connection show -active
NAME UUID TYPE DEVICE
virbr0-nic e9279275-54b8-48ef-a756-d4d714bcd5ac generic virbr0-nic
virbr0 b7af90bc-8003-49df-bf58-4180828be0fd bridge virbr0
Wired connection 2 e3d708dc-aefd-41ea-96d2-81bdd0d307b7 802-3-ethernet ens37
Wired connection 1 8b3b2e8a-1e5d-4982-93d0-77f7fe4eba6a 802-3-ethernet ens38
default 4f8fe83d-df38-4441-83ae-0d400f76c43d 802-3-ethernet ens33

- list all configuration setting for the interace
[root@ashok ~]# nmcli con show "Wired connection 1"
connection.id: Wired connection 1
connection.uuid: 8b3b2e8a-1e5d-4982-93d0-77f7fe4eba6a
connection.interface-name: --
connection.type: 802-3-ethernet
connection.autoconnect: yes

- [root@ashok ~]# nmcli dev status
DEVICE TYPE STATE CONNECTION
virbr0 bridge connected virbr0
ens33 ethernet connected default
ens37 ethernet connected Wired connection 2
ens38 ethernet connected Wired connection 1
virbr0-nic tap connected virbr0-nic
lo loopback unmanaged --

- display device status
[root@ashok ~]# nmcli dev show ens38
GENERAL.DEVICE: ens38
GENERAL.TYPE: ethernet
GENERAL.HWADDR: 00:0C:29:80:C1:E6
GENERAL.MTU: 1500
GENERAL.STATE: 100 (connected)
GENERAL.CONNECTION: Wired connection 1
GENERAL.CON-PATH: /org/freedesktop/NetworkManager/ActiveConnection/1
WIRED-PROPERTIES.CARRIER: on
IP4.ADDRESS[1]: 192.168.10.17/24
IP4.GATEWAY: 192.168.10.1
IP4.DNS[1]: 192.168.10.1
IP6.ADDRESS[1]: fe80::20c:29ff:fe80:c1e6/64
IP6.GATEWAY:
[root@ashok ~]#

2. Assign static ip/gateway/dns on one of the interface
- adding ip/gateway
[root@ashok ~]# nmcli con add con-name eth-ens38 ifname ens38 type ethernet ip4 192.168.10.220/24 gw4 192.168.10.1
Connection 'eth-ens38' (23d86e57-2fae-480f-8015-4ea7a8539812) successfully added.
[root@ashok ~]#

- adding nameserver
[root@ashok ~]# nmcli con mod "eth-ens38" ipv4.dns 192.168.10.110

3. Bring up the interface.

- list connections on the system
[root@ashok ~]# nmcli connection show
NAME UUID TYPE DEVICE
eth-ens38 23d86e57-2fae-480f-8015-4ea7a8539812 802-3-ethernet --
Wired connection 1 8b3b2e8a-1e5d-4982-93d0-77f7fe4eba6a 802-3-ethernet ens38
15dd-442e-bc69-25c5bf2c1b6b 802-3-ethernet --

- bring up the interface
[root@ashok ~]# nmcli con up eth-ens38

- list the active interface
[root@ashok ~]# nmcli con show --active
NAME UUID TYPE DEVICE
eth-ens38 23d86e57-2fae-480f-8015-4ea7a8539812 802-3-ethernet ens38

- verify the ip address

[root@ashok ~]# ip addr show ens38
4: ens38: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:0c:29:80:c1:e6 brd ff:ff:ff:ff:ff:ff
inet 192.168.10.220/24 brd 192.168.10.255 scope global ens38
valid_lft forever preferred_lft forever
inet6 fe80::20c:29ff:fe80:c1e6/64 scope link
valid_lft forever preferred_lft forever
[root@ashok ~]#

4. Reboot the system and verify that your assigned ip address is still available.

- upon rebooting the system, verify the ip address is available.

# ifconfig -a
# ip addr show

[root@ashok ~]# ip route
default via 192.168.10.1 dev ens33 proto static metric 100
192.168.10.0/24 dev ens38 proto kernel scope link src 192.168.10.220 metric 102
[root@ashok ~]#A

[root@ashok ~]# ping -c 2 yahoo.com
PING yahoo.com (98.138.253.109) 56(84) bytes of data.
64 bytes from ir1.fp.vip.ne1.yahoo.com (98.138.253.109): icmp_seq=1 ttl=52 time=53.9 ms

adding disk on vmware RHEL7

1. add the disk on vmware

2. Scan the disk

[root@ashok ~]# echo "- - -"> /sys/class/scsi_host/host0/scan

[root@ashok ~]# echo "- - -"> /sys/class/scsi_host/host1/scan

[root@ashok ~]# echo "- - -"> /sys/class/scsi_host/host2/scan

[root@ashok ~]# fdisk -l

Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0x000bdad6

Device Boot Start End Blocks Id System

/dev/sda1 * 2048 1026047 512000 83 Linux

/dev/sda2 1026048 41943039 20458496 8e Linux LVM

Disk /dev/mapper/centos-root: 10.7 GB, 10737418240 bytes, 20971520 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/centos-swap: 3221 MB, 3221225472 bytes, 6291456 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/centos-home: 6983 MB, 6983516160 bytes, 13639680 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

[root@ashok ~]# fdisk /dev/sdb

Command (m for help): n

Partition type:

p primary (1 primary, 0 extended, 3 free)

e extended

Select (default p):

Using default response p

Partition number (2-4, default 2):

First sector (411648-4194303, default 411648):

Using default value 411648

Last sector, +sectors or +size{K,M,G} (411648-4194303, default 4194303): +200M

Partition 2 of type Linux and of size 200 MiB is set

Command (m for help): n

Partition type:

p primary (2 primary, 0 extended, 2 free)

e extended

Select (default p): p

Partition number (3,4, default 3):

First sector (821248-4194303, default 821248):

Using default value 821248

Last sector, +sectors or +size{K,M,G} (821248-4194303, default 4194303): +200M

Partition 3 of type Linux and of size 200 MiB is set

Command (m for help): p

Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0xc3e9fc2d

Device Boot Start End Blocks Id System

/dev/sdb1 2048 411647 204800 83 Linux

/dev/sdb2 411648 821247 204800 83 Linux

/dev/sdb3 821248 1230847 204800 83 Linux

Command (m for help): n

Partition type:

p primary (3 primary, 0 extended, 1 free)

e extended

Select (default e):

Using default response e

Selected partition 4

First sector (1230848-4194303, default 1230848):

Using default value 1230848

Last sector, +sectors or +size{K,M,G} (1230848-4194303, default 4194303):

Using default value 4194303

Partition 4 of type Extended and of size 1.4 GiB is set

Command (m for help): p

Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0xc3e9fc2d

Device Boot Start End Blocks Id System

/dev/sdb1 2048 411647 204800 83 Linux

/dev/sdb2 411648 821247 204800 83 Linux

/dev/sdb3 821248 1230847 204800 83 Linux

/dev/sdb4 1230848 4194303 1481728 5 Extended

Command (m for help): n

All primary partitions are in use

Adding logical partition 5

First sector (1232896-4194303, default 1232896):

Using default value 1232896

Last sector, +sectors or +size{K,M,G} (1232896-4194303, default 4194303): +200M

Partition 5 of type Linux and of size 200 MiB is set

Command (m for help): n

All primary partitions are in use

Adding logical partition 6

First sector (1644544-4194303, default 1644544):

Using default value 1644544

Last sector, +sectors or +size{K,M,G} (1644544-4194303, default 4194303): +200M

Partition 6 of type Linux and of size 200 MiB is set

Command (m for help): p

Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0xc3e9fc2d

Device Boot Start End Blocks Id System

/dev/sdb1 2048 411647 204800 83 Linux

/dev/sdb2 411648 821247 204800 83 Linux

/dev/sdb3 821248 1230847 204800 83 Linux

/dev/sdb4 1230848 4194303 1481728 5 Extended

/dev/sdb5 1232896 1642495 204800 83 Linux

/dev/sdb6 1644544 2054143 204800 83 Linux

Command (m for help): m

Command action

a toggle a bootable flag

b edit bsd disklabel

c toggle the dos compatibility flag

d delete a partition

g create a new empty GPT partition table

G create an IRIX (SGI) partition table

l list known partition types

m print this menu

n add a new partition

o create a new empty DOS partition table

p print the partition table

q quit without saving changes

s create a new empty Sun disklabel

t change a partition's system id

u change display/entry units

v verify the partition table

w write table to disk and exit

x extra functionality (experts only)

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.

[root@ashok ~]# fdisk -l

Disk /dev/sda: 21.5 GB, 21474836480 bytes, 41943040 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0x000bdad6

Device Boot Start End Blocks Id System

/dev/sda1 * 2048 1026047 512000 83 Linux

/dev/sda2 1026048 41943039 20458496 8e Linux LVM

Disk /dev/mapper/centos-root: 10.7 GB, 10737418240 bytes, 20971520 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/centos-swap: 3221 MB, 3221225472 bytes, 6291456 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/centos-home: 6983 MB, 6983516160 bytes, 13639680 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0xc3e9fc2d

Device Boot Start End Blocks Id System

/dev/sdb1 2048 411647 204800 83 Linux

/dev/sdb2 411648 821247 204800 83 Linux

/dev/sdb3 821248 1230847 204800 83 Linux

/dev/sdb4 1230848 4194303 1481728 5 Extended

/dev/sdb5 1232896 1642495 204800 83 Linux

/dev/sdb6 1644544 2054143 204800 83 Linux

[root@ashok ~]# mkf

mkfifo mkfontscale mkfs.btrfs mkfs.ext2 mkfs.ext4 mkfs.minix mkfs.vfat

mkfontdir mkfs mkfs.cramfs mkfs.ext3 mkfs.fat mkfs.msdos mkfs.xfs

[root@ashok ~]# mkfs

mkfs mkfs.cramfs mkfs.ext3 mkfs.fat mkfs.msdos mkfs.xfs

mkfs.btrfs mkfs.ext2 mkfs.ext4 mkfs.minix mkfs.vfat

[root@ashok ~]# mkfs.xfs /dev/sdb1

meta-data=/dev/sdb1 isize=256 agcount=4, agsize=12800 blks

= sectsz=512 attr=2, projid32bit=1

= crc=0 finobt=0

data = bsize=4096 blocks=51200, imaxpct=25

= sunit=0 swidth=0 blks

naming =version 2 bsize=4096 ascii-ci=0 ftype=0

log =internal log bsize=4096 blocks=853, version=2

= sectsz=512 sunit=0 blks, lazy-count=1

realtime =none extsz=4096 blocks=0, rtextents=0

[root@ashok ~]# blkid /dev/sdb1

/dev/sdb1: UUID="1f25b100-13bc-4f91-957a-4eea740bc9f1" TYPE="xfs"

[root@ashok ~]# mount UUID="1f25b100-13bc-4f91-957a-4eea740bc9f1" /mnt

[root@ashok ~]# cd /mnt

[root@ashok mnt]# ls

[root@ashok mnt]# mkdir newdir

[root@ashok mnt]# ls

newdir

[root@ashok mnt]# touch this is so cool and I am liking it

[root@ashok mnt]# ls -ltr

total 0

drwxr-xr-x. 2 root root 6 Jan 3 17:23 newdir

-rw-r--r--. 1 root root 0 Jan 3 17:23 this

-rw-r--r--. 1 root root 0 Jan 3 17:23 is

-rw-r--r--. 1 root root 0 Jan 3 17:23 so

-rw-r--r--. 1 root root 0 Jan 3 17:23 cool

-rw-r--r--. 1 root root 0 Jan 3 17:23 and

-rw-r--r--. 1 root root 0 Jan 3 17:23 liking

-rw-r--r--. 1 root root 0 Jan 3 17:23 I

-rw-r--r--. 1 root root 0 Jan 3 17:23 am

-rw-r--r--. 1 root root 0 Jan 3 17:23 it

[root@ashok mnt]# pwd

/mnt

[root@ashok mnt]# cd /

[root@ashok /]# df -h /mnt

Filesystem Size Used Avail Use% Mounted on

/dev/sdb1 197M 11M 187M 6% /mnt

[root@ashok /]# umount /mnt

[root@ashok /]# df -h /mnt

Filesystem Size Used Avail Use% Mounted on

/dev/mapper/centos-root 10G 3.7G 6.4G 37% /

[root@ashok /]# cd /mnt

[root@ashok mnt]# ls

[root@ashok mnt]# ls -l

total 0

[root@ashok mnt]# cd

[root@ashok ~]# mount UUID="1f25b100-13bc-4f91-957a-4eea740bc9f1" /mnt

[root@ashok ~]# cd /mnt

[root@ashok mnt]# ls

am and cool I is it liking newdir so this

[root@ashok mnt]#

894 find /home -user ashok

895 find /home -group ashok

896 grep ashok /etc/group

897 find /home -group kamal

898 find /home -group devi

899 find / -user kamal -group devi

900 find /home -perm -777

901 find /home -perm -222

902 ls -l /home/ashok/n1234 /home/ashok/aaaaa /home/andy/a

903 find /home -perm -111

904 ls -l /home/andy/.mozilla/extensions

905 ls -ld /home/andy/.mozilla/extensions

906 find /home -perm -777

907 ls -l /home/ashok/.mozilla/firefox/qpi9jfhh.default/lock

908 p

909 mkdir /home/abc

910 chmod 777 /home/abc

911 find /home -perm -777

912 pwd

913 find /home -size 2M

914 find /home -size 2M -exec ls -l {} \;

915 find /home -size 2M -exec ls -lh {} \;

916 grep 1000 /etc/group

917 groupadd -g 1000 ashok1

918 find /home -size 2M -exec ls -lh {} \;

919 groupdel ashok1

920 find /home -size 2M -exec ls -lh {} \;

921 find /home -mtime -130

922 find /home -mmin -130

923 ls -l

924 find . -type f -links +1

925 pwd

926 df -l

927 fdisk -l

928 fdisk

929 fdisk -l

930 lshw

931 echo "- - -"> /sys/class/scsi_host/host0/scan

932 echo "- - -"> /sys/class/scsi_host/host1/scan

933 echo "- - -"> /sys/class/scsi_host/host2/scan

934 fdisk -l

935 fdisk

936 fdisk -cu /dev/sdb

937 fdisk /dev/sdb

938 fdisk -l

939 mkfs.xfs /dev/sdb1

940 blkid /dev/sdb1

941 mount UUID="1f25b100-13bc-4f91-957a-4eea740bc9f1" /mnt

942 cd /mnt

943 ls

944 mkdir newdir

945 ls

946 touch this is so cool and I am liking it

947 ls -ltr

948 pwd

949 cd /

950 df -h /mnt

951 umount /mnt

952 df -h /mnt

953 cd /mnt

954 ls

955 ls -l

956 cd

957 mount UUID="1f25b100-13bc-4f91-957a-4eea740bc9f1" /mnt

958 cd /mnt

959 ls

960 history

[root@ashok mnt]#

3. create a partition