Linux OS Dev

Kernel programming for Linux operating systems can be done with many different languages; C, C++, Python, Perl and Java, which are some of the most common languages used.There are also many different varieties of Linux, such as Ubuntu, Fedora and OpenSUSE.

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I  have a few question for selection of drop policy applied place.

1. Which one first apply the drop rule ?
2. iptables and nftables are user space appliances but i do not know deeper , are they work in kernel space and pipe the requests from user space or are they work completely after kernel space ?
3. Is there any possibility to drop a packet before any kernel space module ,i tryed with netfilter and drop an ip xx.xx.xx.xx and i realize that tcpdump still reading the traffic but iptables not. So the traffic is passing to kernel space still on netfilter.
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FREE GUIDES: In-depth and hand-crafted Linux, AWS, OpenStack, DevOps, Azure, and Cloud training guides created by Linux Academy instructors and the community.

how can I see all packages that are installed in a Ubuntu instance?

Error: Package: R-core-devel-3.4.0-2.el6.x86_64
           Requires: libicu-devel
yum can be configured to try to resolve such errors by temporarily enabling
disabled repos and searching for missing dependencies.
To enable this functionality please set 'notify_only=0' in /etc/yum/pluginconf.d/search-disabled-repos.conf

--> Running transaction check
---> Package R-core-devel.x86_64 0:3.4.0-2.el6 will be an update
--> Processing Dependency: libicu-devel for package: R-core-devel-3.4.0-2.el6.x86_64
---> Package kernel.x86_64 0:2.6.32-642.11.1.el6 will be erased
--> Finished Dependency Resolution
Error: Package: R-core-devel-3.4.0-2.el6.x86_64
           Requires: libicu-devel
 You could try using --skip-broken to work around the problem
** Found 2 pre-existing rpmdb problem(s), 'yum check' output follows:
tomcat6-admin-webapps-6.0.24-98.el6_8.noarch has missing requires of tomcat6 = ('0', '6.0.24', '98.el6_8')
tomcat6-webapps-6.0.24-98.el6_8.noarch has missing requires of tomcat6 = ('0', '6.0.24', '98.el6_8')
Hi, please need guidance on how to fix the npm error. Thanks so much in advance.

# rpm --query centos-release

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# node --version

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# npm --version

    throw err;
Error: Cannot find module 'npmlog'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at /usr/lib/node_modules/npm/bin/npm-cli.js:18:11
    at Object.<anonymous> (/usr/lib/node_modules/npm/bin/npm-cli.js:86:3)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)

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Hi guys.

I wrote a little Bash script (That works together with Some Python Scripts)
to help me manage the number of tickets opened to the system administrators team.

When running the script manually, it works perfectly.

However, when I wrapped it into a service unit and a timer unit, something odd happens.
The script runs - I can see the output in the logs. I can hear the sound alert but I don't see the notify window popping up on the screen.

Here is the bash script:
export DISPLAY=":1"
/usr/bin/kill $(/usr/bin/pidof yad) 2>/dev/null
TTIM=$(/home/david/scripts/ # Holds the number of tickets in the mailbox (TIM = Tickets in mailbox)
LTC=$(cat /home/david/scripts/count.txt) #Holds the last ticket count. (LTC = Last Ticket Count)
UTIM=$(/home/david/scripts/ # Holds the number of Unread Tickets in the mailbox

if (( $TTIM < $LTC )) # If the number of tickets in the mailbox is lower than the Last Count, update the last count and check for unread mails.
		echo $TTIM >  /home/david/scripts/count.txt
		if ((  UTIM =0 ))
				echo "There are $TTIM in the mailbox COND 1" >> /home/david/scripts/run.log
				/usr/bin/notify-send "There are no new Tickets! There are $TTIM tickets opened!"
				exit 0
if (( $UTIM > 0 )) #If there are any unread tickets, throw the message anyway!
		echo $TTIM >  /home/david/scripts/count.txt
		/usr/bin/aplay /home/david/scripts/1.wav;
		echo "There are $TTIM in the mailbox 

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I have linux application account and  would like to restrict the user to login directly. I want this account to be under sudoers. users can login and sudo into this account. How do i do that in linux?
Imagine the following scenario:

A NAS box, providing a samba share, with several versions of a fíle collection in dated directories (name i.e. "2017.05.24").

On the NAS should be some links into subdirectories of the latest version, so the copy script should create symbolic links on the share to the latest version of that file collection.

When I try
ln -s <samba_share/link_name> <samba_share/dated_dir_subdir/>

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I get an error that this is not possible. Any hint ?
Hi guys,

Although I find it hard to believe that what I'm looking for even exists, I'll still try my luck.

Is there any Linux Based IDE with native support for bash scripting?
(I don't only mean things like syntax highlighting but also auto completion and etc.) and preferably with git support.

Is there anyway to get a compiled bytecode from a bash script? I know about SHC but it doesn't really help becasue reversing it is way to easy - there's already a ready shell script to reverse the SHC compilation called UNSHC.

what are the best practices and features, options while using grep.

i am using these days to search in log files, files, directories, content etc

When should i give single quote '  '
zgrep 'xyz' aaa.gz

When should i give double quote " "
zgrep "xyz" aaa.gz

how to use tail and head etc along with grep to effectively monitor last or first 100 lines etc
please advise

I keep getting below error when i wrote shell script file and try to open it to.

Swap file "" already exists!
[O]pen Read-Only, (E)dit anyway, (R)ecover, (Q)uit, (A)bort:

why it created .swp file autoatically?
why it asks above question. How to tell unix not to ask that question.
please advise
How to Create Failover DNS Record Sets in Route 53
How to Create Failover DNS Record Sets in Route 53

Route 53 has the ability to easily configure DNS record sets specifically for failover scenarios. These failover record sets can be configured to failover to full-blown deployments in other regions or to a static HTML page that informs your customers of the issue.

what are differences between
user defined, environmental. local, global variables

when to use which one. what are advanatages, disadvantages of using each with practical examples.
please advise

I like to write a unix shell script to check calendar year, date, current working directory.

how to write and shave .sh file(Say and how to execute to see the output.

Any detailed link explaining these steps with screenshots. please advise

I like to delete matched pattern in a file using vi editor and sed command

i tried as below not working

$ sed 'hello' aaaa.txt :%

please advise
I am trying to build nodejs from source code.

WARNING: C++ compiler too old, need g++ 4.8 or clang++ 3.4 (CXX=g++)
creating ./icu_config.gypi
* Using ICU in deps/icu-small
Using version-specific floating patch tools/icu/patches/58/source/i18n/digitlst.cpp
creating ./icu_config.gypi
{ 'target_defaults': { 'cflags': [],
                       'default_configuration': 'Release',
                       'defines': [],
                       'include_dirs': [],
                       'libraries': []},
  'variables': { 'asan': 0,
                 'coverage': 'false',
                 'debug_devtools': 'node',
                 'force_dynamic_crt': 0,
                 'gas_version': '2.20',
                 'host_arch': 'x64',
                 'icu_data_file': 'icudt58l.dat',
                 'icu_data_in': '../../deps/icu-small/source/data/in/icudt58l.dat',
                 'icu_endianness': 'l',
                 'icu_gyp_path': 'tools/icu/icu-generic.gyp',
                 'icu_locales': 'en,root',
                 'icu_path': 'deps/icu-small',
                 'icu_small': 'true',
                 'icu_ver_major': '58',
                 'node_byteorder': 'little',
                 'node_enable_d8': 'false',
                 'node_enable_v8_vtunejit': 'false',
                 'node_install_npm': 'true',
                 'node_module_version': 48,
                 'node_no_browser_globals': 'false',
                 'node_prefix': '/usr/local',
I am running redhat linux 6.8

i want to build a new RPM using the source code of nodejs (6.10)

As i am new to RPB build, i am looking for assistance with creating RPM.
as per the output below i am getting some waiting for an event.  every time it is stuck at poll As i have limited skills in strace, can some one guide me to find the root cause of the slowness.

munmap(0x7f14322fb000, 4096)            = 0
connect(5, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("10.x.x.1")}, 16) = 0
poll([{fd=5, events=POLLOUT}], 1, 0)    = 1 ([{fd=5, revents=POLLOUT}])
sendto(5, ">a\1\0\0\1\0\0\0\0\0\0\trhn1-01-c\5myc\2ca\0"..., 36, MSG_NOSIGNAL, NULL, 0) = 36
poll([{fd=5, events=POLLIN|POLLOUT}], 1, 5000) = 1 ([{fd=5, revents=POLLOUT}])
sendto(5, "\242:\1\0\0\1\0\0\0\0\0\0\trhn1-01-c\myc\2ca\0"..., 36, MSG_NOSIGNAL, NULL, 0) = 36
poll([{fd=5, events=POLLIN}], 1, 4999

[root@ tmp]# strace -e poll yum repolist
Loaded plugins: product-id, search-disabled-repos, security, subscription-manager
poll([{fd=5, events=POLLIN}], 1, 10)    = 1 ([{fd=5, revents=POLLIN}])
poll([{fd=5, events=POLLOUT}], 1, 0)    = 1 ([{fd=5, revents=POLLOUT}])
poll([{fd=5, events=POLLIN|POLLOUT}], 1, 5000) = 1 ([{fd=5, revents=POLLOUT}])
poll([{fd=5, events=POLLIN}], 1, 4999)  = 0 (Timeout)
poll([{fd=6, events=POLLOUT}], 1, 0)    = 1 ([{fd=6, revents=POLLOUT}])
poll([{fd=6, events=POLLIN|POLLOUT}], 1, 5000) = 1 ([{fd=6, revents=POLLOUT}])
poll([{fd=6, events=POLLIN}], 1, 4999)  = 1 ([{fd=6, revents=POLLIN}])
poll([{fd=6, events=POLLIN}], 1, 4999)  = 1 ([{fd=6, revents=POLLIN}])
poll([{fd=6, …
My  VMware machine is not booting.
"vsd-mount                      [!!]
you have entered the recovery shell. the situation you are in may be recoverable.
if you are able to fix this situation the boot process will continue normally after you exit this terminal
/bin/sh: can't access tty; job control turned off"
Hello Folks,

I have a script *.sh That I like to install to few machines (IPs Address), is there anyway anybody can help me write script to do multiples at the same time ?

By the way I'm currently using centos x64

I'd appreciate it and thanks for looking
i have some old unix disks that are on 3.5 and i need to access the data on them, i have loaded up linux and hae been trying to load them but to no success have tried
$ mkdir /mnt/floppy
working through this page

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

I have the following output i want to write a python code to read only $### and store in a list.

Dining ...2121$15.81
Open Drawer3/14/17
Dining ...2121$5.65
Open Drawer3/14/17
Tim Hortons Tim Hortons
Dining ...2121$5.60
Open Drawer3/11/17
Dining ...2121$8.76
Open Drawer3/11/17
output omitted.
Hi Guys,

Machines on my network recently updated to version 52, which has caused a lot of problems, i managed to get a copy of the 51 deb, but there are one or two machines, when after running "purge firefox" and trying to install version 51 from running dpkg -i firefox.deb it just wont install, if i do apt-get install firefox it works, but only version 52.

I am connecting to these machines over netcat
Dear Experts

I have installed rhel7 and httpd24, rh-php56 and mysql56 this is required for sugarcrm7.8 with the default repos and as well additional with the  repo  rhscl I am not getting the php56-php-mcrypt , without this it is not becoming possible to install the Sugarcrm7.8, can you please suggest where I can get the package php56-php-mcrypt. thanks in advance
I am logged into Linux box and I am not good in commands

I am attaching screen shot, I need to select continent, time zone

I don't know  what next steps to take,

can some body guide me in taking what key board steps
My computer is running Windows 10 Pro, 64-bit.  My C language files or my code (program) are stored in the hard disk.  

The old and new version of WindRiver Diab Compiler are stored in Linux Server?

My bash profile used to contain path to old compiler.  To compile, I ran Winscp to access Linux Server.  Then, I dragged my C language project to Linux Server.  I opened the command window from Winscp and invoked make program to build my executables.  This all worked fine.

To build with new compiler, I changed path in my bash profile but my code (program) is still getting build with old compiler.  The generated .map file shows path to old compiler.

My bash profile is stored in my windows desktop.  Does Winscp read bash profile when it is invoked?  How does it know to read bash profile from desktop?  Why is my program not getting built with new compiler?
in bash file i have a if statement

if [err -gt 0] then  # if err greather that 0
elsif [war -gt 0] then
elseif [rng -gt 0] then
else stat=OK

syntax error near unexpected token `else'
'else stat=OK'

what is wrong her

Linux OS Dev

Kernel programming for Linux operating systems can be done with many different languages; C, C++, Python, Perl and Java, which are some of the most common languages used.There are also many different varieties of Linux, such as Ubuntu, Fedora and OpenSUSE.

Top Experts In
Linux OS Dev