Learn watch command to execute script or shell commands repeatedly every n seconds. Very much useful in automation or monitoring.
watch command and its examples
watch command is a small utility using which you can execute shell command or script repetitively and after every n seconds. Its helpful in automation or monitoring. Once can design automation by monitoring some code/command output using watch to trigger next course of action e.g. notification.
watch command is part of procpspackage. Its bundled with OS still you can verify if package is installed on the system. This utility can be used directly by issuing the watch command followed by command/script name to execute.
Watch command in action
For example, I created a small script which writes junk data continuously in a file placed under /. This will change utilization numbers in df -k output. In the above GIF, you can see changes in the “Used” and “Available” column of df -k output when monitored with watch command.
In output, you can see –
The default time interval is 2 seconds as shown n first line
Time duration followed by a command which is being executed by watch
The current date, time of server on the right-hand side
Output of command being executed
Go through below watch command examples to understand how flexible the watch is.
Different options of watch
Now, to change the default time interval use option -n followed by time interval of your choice. To execute command after 20 seconds you can use :
# watch -n 20 df -k
Every 20.0s: df -k Mon Mar 20 15:00:47 2017
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/xvda1 6061632 2194812 3552248 39% /
tmpfs 509252 0 509252 0% /dev/shm
See above output, interval is changed to 20 seconds (highlighted row)
If you want to hide header in output i.e. time interval, the command being executed, and current server date, time, use -t option. It will strip off the first line of output.
# watch -t df -h
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/xvda1 6061632 2194812 3552248 39% /
tmpfs 509252 0 509252 0% /dev/shm
Highlighting difference in the present and previous output is made easy with -d option. To understand this, watch below GIF –
watch command with -d option
In the above output, I used the same data writing script to fill /. You can observe the only portion which is different from the previous output is being highlighted by watch in the white box!
On-demand NFS mounting utility: autofs. Learn what is autofs, why, and when to use autofs and autofs configuration steps in the Linux server.
Autofs configuration
The first place to manage mount points on any Linux system is /etc/fstab file. These files mount all listed mount points at the system startup and made them available to the user. Although I explained mainly how autofs advantages us with NFS mount points, it also works well with native mount points.
NFS mount points are also part of it. Now, the issue is even if users don’t access NFS mount points they are still mounted by /etc/fstab and leech some system resources in the background continuously. Like NFS services need to check connectivity, permissions, etc details of these mount points in the background continuously. If these NFS mounts are considerably high in numbers then managing them through /etc/fstab will be a major drawback since you are allotting major system resource chunk to system portion which is not frequently used by users.
Why use AutoFS?
In such a scenario, AutoFS comes in picture. AutoFS is on-demand NFS mounting facility. In short, it mounts NFS mount points when a user tries to access them. Again once time hits timeout value (since last activity on that NFS mount), it will automatically un-mount that NFS mount saving system resources serving idle mount point.
It also reduces your system boot time since the mounting task is done after system boot and when the user demands it.
When use AutoFS?
If your system is having a large number of mount points
Many of them are not being used frequently
The system is tight on resources and every single piece of system resource counts
AutoFS configuration steps
First, you need to install package autofs using yum or apt. The main configuration file for autofs is /etc/auto.masterwhich is also called a mast map file. This file has autofs controlled mount points details. The master file follows below format :
mount_point map_file options
where –
mount_point is a directory on which mounts should be mounted
map_file (automounter map file) is a file containing a list of mount points and their file systems from which they should be mounted
options are extra options to be applied on mount_point
Sample master map file looks like one below :
/my_auto_mount /etc/auto.misc --timeout=60
In above sample, mount points defined under /etc/auto.misc files can be mounted on /my_auto_mount directory with timeout value 60 sec.
Parameter map_file (automounter map file) in the above master map file is also a configuration file which has below format :
mount_point options source_location
where –
mount_point is a directory on which mounts should be mounted
options are mounting options
source_location is FS or NFS path from where the mount will be mounted
Sample automounter map file looks like one below :
linux -ro,soft,intr ftp.example.org:/pub/linux
data1 -fstype=ext3 :/dev/fd0
Users should be aware of the share path. Means, in our case, /my_auto_mount and Linux, data1 these paths should be known to users in order to access them.
In all both these configuration file collectively tells :
Whenever user tries to access mount point Linux or data1 –
autofs checks data1 source (/dev/fs0) with option (-fstype=ext3)
mounts data1 on /my_auto_mount/data1
Un-mounts /my_auto_mount/data1 when there is no activity on mount for 60 secs
Once you are done with configuring your required mounts you can start autofs service. Reload its configurations :
# /etc/init.d/autofs reload
Reloading maps
That’s it! Configuration is done!
Testing AutoFS configuration
Once you reload configuration, check and you will notice autofs defined mount points are not mounted on systems (output of df -h).
Now cd into /my_auto_mount/data1 and you will be presented with a listing of the content of data1 from /dev/fd0!
Another way is to use watch utility in another session and keep watch on command mount. As you execute commands, you will see mount point is mounted on system and after timeout value it’s un-mounted!
Understand AWS cloud terminology of 71 services! Get acquainted with terms used in the AWS world to start with your AWS cloud career!
AWS Cloud terminology
AWS i.e. Amazon Web Services cloud platform providing list of web services on pay per use basis. It’s one of the famous cloud platforms to date. Due to flexibility, availability, elasticity, scalability, and no-maintenance, many corporations are moving to the cloud. Since many companies using these services, it becomes necessary that sysadmin or DevOps should be aware of AWS.
This article aims at listing services provided by AWS and explaining the terminology used in the AWS world.
As of today, AWS offers a total of 71 services which are grouped together in 17 groups as below :
Compute
It’s a cloud computing means virtual server provisioning. This group provides the below services.
EC2 container service: Its high performance, highly scalable which allows running services on EC2 clustered environment
Lightsail: This service enables the user to launch and manage virtual servers (EC2) very easily.
Elastic Beanstalk: This service manages capacity provisioning, load balancing, scaling, health monitoring of your application automatically thus reducing your management load.
Lambda: It allows you to run your code only when needed without managing servers for it.
Batch: It enables users to run computing workloads (batches) in a customized managed way.
Storage
It’s cloud storage i.e. cloud storage facility provided by Amazon. This group includes :
S3: S3 stands for Simple Storage Service (3 times S). This provides you online storage to store/retrieve any data at any time, from anywhere.
EFS: EFS stands for Elastic File System. It’s online storage that can be used with EC2 servers.
Glacier: Its a low cost/slow performance data storage solution mainly aimed at archives or long term backups.
Storage Gateway: Its interface which connects your on-premise applications (hosted outside AWS) with AWS storage.
Database
AWS also offers to host databases on their Infra so that clients can benefit from cutting edge tech Amazon have for faster/efficient/secured data processing. This group includes :
RDS: RDS stands for Relational Database Service. Helps to set up, operate, manage a relational database on cloud.
DynamoDB: Its NoSQL database providing fast processing and high scalability.
ElastiCache: It’s a way to manage in-memory cache for your web application to run them faster!
Redshift: It’s a huge (petabyte-size) fully scalable, data warehouse service in the cloud.
Networking & Content Delivery
As AWS provides a cloud EC2 server, its corollary that networking will be in the picture too. Content delivery is used to serve files to users from their geographically nearest location. This is pretty much famous for speeding up websites nowadays.
VPC: VPC stands for Virtual Private Cloud. It’s your very own virtual network dedicated to your AWS account.
CloudFront: Its content delivery network by AWS.
Direct Connect: Its a network way of connecting your datacenter/premises with AWS to increase throughput, reduce network cost, and avoid connectivity issues that may arise due to internet-based connectivity.
Route 53: Its a cloud domain name system DNS web service.
Migration
Its a set of services to help you migrate from on-premises services to AWS. It includes :
Application Discovery Service: A service dedicated to analyzing your servers, network, application to help/speed up the migration.
DMS: DMS stands for Database Migration Service. It is used to migrate your data from on-premises DB to RDS or DB hosted on EC2.
Server Migration: Also called SMS (Server Migration Service) is an agentless service that moves your workloads from on-premises to AWS.
Snowball: Intended to use when you want to transfer huge amount of data in/out of AWS using physical storage appliances (rather than internet/network based transfers)
Developer Tools
As the name suggests, its a group of services helping developers to code easy/better way on the cloud.
CodeCommit: Its a secure, scalable, managed source control service to host code repositories.
CodeBuild: Code builder on the cloud. Executes tests codes and build software packages for deployments.
CodeDeploy: Deployment service to automate application deployments on AWS servers or on-premises.
CodePipeline: This deployment service enables coders to visualize their application before release.
X-Ray: Analyse applications with event calls.
Management Tools
Group of services which helps you manage your web services in AWS cloud.
CloudWatch: Monitoring service to monitor your AWS resources or applications.
CloudFormation: Infrastructure as a code! It’s a way of managing AWS relative infra in a collective and orderly manner.
CloudTrail: Audit & compliance tool for AWS account.
Config: AWS resource inventory, configuration history, and configuration change notifications to enable security and governance.
OpsWorks: Automation to configure, deploy EC2 or on-premises compute
Service Catalog: Create and manage IT service catalogs which are approved to use in your/company account
Trusted Advisor: Its AWS AI helping you to have better, money-saving AWS infra by inspecting your AWS Infra.
Managed Service: Provides ongoing infra management
Security, Identity & compliance
Important group of AWS services helping you secure your AWS space.
IAM: IAM stands for Identity and Access Management. Controls user access to your AWS resources and services.
Inspector: Automated security assessment helping you to secure and compliance your apps on AWS.
Certificate Manager: Provision, manage, and deploy SSL/TLS certificates for AWS applications.
Directory Service: Its Microsoft Active Directory for AWS.
WAF & Shield: WAF stands for Web Application Firewall. Monitors and controls access to your content on CloudFront or Load balancer.
Compliance Reports: Compliance reporting of your AWS infra space to make sure your apps and the infra are compliant with your policies.
Analytics
Data analytics of your AWS space to help you see, plan, act on happenings in your account.
Athena: Its a SQL based query service to analyze S3 stored data.
EMR: EMR stands for Elastic Map Reduce. Service for big data processing and analysis.
CloudSearch: Search capability of AWS within application and services.
Elasticsearch Service: To create a domain and deploy, operate, and scale Elasticsearch clusters in the AWS Cloud
Kinesis: Stream’s large amounts of data in real-time.
Data Pipeline: Helps to move data between different AWS services.
QuickSight: Collect, analyze, and present insight into business data on AWS.
Artificial Intelligence
AI in AWS!
Lex: Helps to build conversational interfaces in an application using voice and text.
Polly: Its a text to speech service.
Rekognition: Gives you the ability to add image analysis to applications
Machine Learning: It has algorithms to learn patterns in your data.
Internet of Things
This service enables AWS highly available on different devices.
AWS IoT: It lets connected hardware devices to interact with AWS applications.
Game Development
As name suggest this services aims at Game Development.
Amazon GameLift: This service aims for deploying, managing dedicated gaming servers for session-based multiplayer games.
Mobile Services
Group of services mainly aimed at handheld devices
Mobile Hub: Helps you to create mobile app backend features and integrate them into mobile apps.
Cognito: Controls mobile user’s authentication and access to AWS on internet-connected devices.
Device Farm: Mobile app testing service enables you to test apps across android, iOS on real phones hosted by AWS.
Mobile Analytics: Measure, track, and analyze mobile app data on AWS.
Pinpoint: Targeted push notification and mobile engagements.
Application Services
Its a group of services which can be used with your applications in AWS.
Step Functions: Define and use various functions in your applications
SWF: SWF stands for Simple Workflow Service. Its cloud workflow management helps developers to co-ordinate and contribute at different stages of the application life cycle.
API Gateway: Helps developers to create, manage, host APIs
Elastic Transcoder: Helps developers to converts media files to play of various devices.
Messaging
Notification and messaging services in AWS
SQS: SQS stands for Simple Queue Service. Fully managed messaging queue service to communicate between services and apps in AWS.
SNS: SNS stands for Simple Notification Service. Push notification service for AWS users to alert them about their services in AWS space.
SES: SES stands for Simple Email Service. Its cost-effective email service from AWS for its own customers.
Business Productivity
Group of services to help boost your business productivity.
WorkDocs: Collaborative file sharing, storing, and editing service.
WorkMail: Secured business mail, calendar service
Amazon Chime: Online business meetings!
Desktop & App Streaming
Its desktop app streaming over cloud.
WorkSpaces: Fully managed, secure desktop computing service on the cloud
AppStream 2.0: Stream desktop applications from the cloud.
# make
gcc -DHAVE_CONFIG_H -I. -I. -I. -g -O2 -Wall -Wno-comment -c cmatrix.c
cmatrix.c:37:20: fatal error: curses.h: No such file or directory
#include <curses.h>
^
compilation terminated.
make: *** [cmatrix.o] Error 1
After troubleshooting I came up with a solution and able to pass through make stage. I am sharing it here which might be useful for you.
curses.h header file belongs to ncurses module! You need to install packagesncurses-devel,ncurses (YUM) or libncurses5-dev (APT) and you will be through this error.
Use yum install ncurses-devel ncurses for YUM based systems (like Red Hat, CentOS, etc.) or apt-get install libncurses5-dev for APT based systems (like Debian, Ubuntu, etc.) Verify once that package is installed and proceed with your next course of action.
Learn to check if the package is installed on the Linux server or not. Verify if the package available on the server along with its installed date.
Check if package in installed on Linux
Package installation on Linux sometimes fails with error package is already installed; nothing to do. To avoid this you need to first check if the package is installed on system or not and then attempt its installation. In this article, we will be seeing different ways we can check if the package is installed on the server and also check its installation date.
We are using -qa i.e. query all options which will list all installed packages on the system. We are grepping out our desired (telnet in this example) package name. If the output is blank then the package is not installed. If it’s installed then the respective name will be shown (like above). To understand what these numbers in package name mean read package naming conventions.
Or even directly querying the package name will yield you the same result as the second example above.
If the system is configured with YUM then it can list all installed packages for you and you can grep out your desired package from it.
# yum list installed telnet
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos
Installed Packages
telnet.x86_64 1:0.17-60.el7 @rhui-REGION-rhel-server-releases
OR
# yum list installed |grep telnet
telnet.x86_64 1:0.17-60.el7 @rhui-REGION-rhel-server-releases
On APT based systems
APT based systems like Debian, Ubuntu, etc, dpkg command can be used to verify if the package is installed –
Column wise fields in output are Name, Version, Architecture, Description.
If you have an apt repository configured then you can try to install emulation of the desired package. If it’s installed then the respective message will be shown in output (highlighted line below). If it’s not installed then output just emulates installation process and exits without actually installing. –
# apt-get install -s telnet
Reading package lists... Done
Building dependency tree
Reading state information... Done
telnet is already the newest version (0.17-40).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Package installation date
One of the Linux interview questions is how to find the package installation date? or how to check when the package was installed in Linux? Answer is –
On YUM based systems
rpm command has a direct option of sorting packages with their installed date --last. Grep your desired package and you will get its installed date.
# rpm -qa --last |grep telnet
telnet-0.17-60.el7.x86_64 Fri 10 Mar 2017 01:58:17 PM EST
On APT based systems
Here there is no direct command which shows installation date. You have to grep ‘install’ word through installer log files /var/log/dpkg.log to get the installation date. If logrotate is configured on the system then use wild card * to search through all rotated and current log files.
If you observe this file does not exist on your server then install operation wasn’t performed on that system after its setup. On the very first install operation (using apt-get or dpkg) this file will get created and start logging installation details.
# grep install /var/log/dpkg.log* |grep telnet
2017-03-10 19:26:30 status installed telnet:amd64 0.17-40
2017-03-10 19:26:30 status half-installed telnet:amd64 0.17-40
2017-03-10 19:26:40 install telnet:amd64 0.17-40 0.17-40
2017-03-10 19:26:40 status half-installed telnet:amd64 0.17-40
2017-03-10 19:26:40 status installed telnet:amd64 0.17-40
Article explaining service management in Linux. Learn how to restart service in Linux distro like Red Hat, Debian, Ubuntu, CentOS, etc.
Service management in Linux
Managing services in Linux is one of the frequent task sysadmins need to take care of. In this post, we will be discussing several operations like –
How to stop service in Linux
How to start service in Linux
How to restart service in Linux
How to check the status of service in Linux
Different distributions have different ways of service management. Even within the same distro, different versions may have different service management aspects. Like RHEL 6 and RHEL7 has different commands to manage services.
Let’s see service related tasks in various flavors of Linux –
How to stop service in Linux
Service can be stopped with below commands (respective distro specified)
here <name> is service name like telnet, NTP, NFS, etc. Note that upstart is pre-installed with Ubuntu 6.10 later, if not you can install using the APT package.
Newer versions are implementing systemctl now in place of service command. Even if you use service command in RHEL7 then it will call systemctl in turns.
# service sshd-keygen status
Redirecting to /bin/systemctl status sshd-keygen.service
● sshd-keygen.service - OpenSSH Server Key Generation
Loaded: loaded (/usr/lib/systemd/system/sshd-keygen.service; static; vendor preset: disabled)
Active: inactive (dead)
-----output clipped-----
In the above output, you can see it shows you which systemctl command its executing in place of service command. Also, note that it appends .service to service_name supplied to service command.
Old service commands like RHEL6 & lower, prints status of operation as OK (success) or FAILED (failure) for start, stop, restart operations. systemctl the command doesn’t print any output on the console.
How to start service in Linux
Starting service follows same above syntax.
# service <name> start (RHEL6 & lower, Ubuntu, CentOS, Debian, Fedora)
# systemctl start <name>.service (RHEL7)
# start <name> (Ubuntu with upstart)
It stops service and then immediately starts it. So basically its a combined command of above two.
Mostly to reload edited new configuration we seek restart of service. But this can be done without restarting it provided service supports reload config. This can be done by using reload option instead of restart.
How to check the status of service in Linux
Checking the status of service makes you aware of if service is currently running or not. Different distros give different details about service in the output of status. Below are a few examples for your reference.
Service status information in Ubuntu :
# service cron status
â cron.service - Regular background program processing daemon
Loaded: loaded (/lib/systemd/system/cron.service; enabled; vendor preset: enabled)
Active: active (running) since Fri 2017-03-10 17:53:23 UTC; 2s ago
Docs: man:cron(8)
Main PID: 3506 (cron)
Tasks: 1
Memory: 280.0K
CPU: 1ms
CGroup: /system.slice/cron.service
ââ3506 /usr/sbin/cron -f
Mar 10 17:53:23 ip-172-31-19-90 systemd[1]: Started Regular background program processing daemon.
Mar 10 17:53:23 ip-172-31-19-90 cron[3506]: (CRON) INFO (pidfile fd = 3)
Mar 10 17:53:23 ip-172-31-19-90 cron[3506]: (CRON) INFO (Skipping @reboot jobs -- not system startup)
It has details about the service state, its man page, PID, CPU & MEM utilization, and recent happenings from the log.
Service status information in RHEL6:
# service crond status
crond (pid 1474) is running...
It only shows you PID and state of service.
Service status information in RHEL7:
# systemctl status crond.service
â crond.service - Command Scheduler
Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
Active: active (running) since Fri 2017-03-10 13:04:58 EST; 1min 2s ago
Main PID: 499 (crond)
CGroup: /system.slice/crond.service
ââ499 /usr/sbin/crond -n
Mar 10 13:04:58 ip-172-31-24-59.ap-south-1.compute.internal systemd[1]: Started Command Scheduler.
Mar 10 13:04:58 ip-172-31-24-59.ap-south-1.compute.internal systemd[1]: Starting Command Scheduler...
Mar 10 13:04:58 ip-172-31-24-59.ap-south-1.compute.internal crond[499]: (CRON) INFO (RANDOM_DELAY will be scaled with factor 85% if used.)
Mar 10 13:04:59 ip-172-31-24-59.ap-south-1.compute.internal crond[499]: (CRON) INFO (running with inotify support)
It prints all details as Ubuntu but doesn’t show CPU and memory utilization, manpage.
List all services on the system
If you want to see all services running on the system and their statuses then you can use below command :
# service --status-all (RHEL6 & lower, Ubuntu, CentOS, Debian, Fedora)
# systemctl list-units --type service --all (RHEL7)
It will present you list of all services and their status with few other details.
Learn how to use two utilities called figlet and toilet to create beautiful ASCII text banners in the Linux terminal. Stylize your terminal!
Beautiful text banners in Linux
Have you seen some stylish ASCII text banners during login on some servers? Or have you seen pages of this blog that have titles written in ASCII? Check out a few styles below too.
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/ \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \ / \
( k | e | r | n | e | l | t | a | l | k | s | . | c | o | m )
\_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|k|e|r|n|e|l|t|a|l|k|s|.|c|o|m|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| _ ._._ _ |_|_ _.|| _ _ _ ._ _
|<(/_| | |(/_| |_(_|||<_>o(_(_)| | |
Beautiful eh? You can create them too with tools called figlet and toilet!
figlet tool
It’s a command-line text styling utility. You need to install figlet package. Once installed you can supply the text you want to stylize to figlet command and it will print stylish output on your terminal. You can copy it and use it anywhere. All the above texts are printed using the figlet only. By default, it will print in below style –
These text banners are useful to stylize your server’s login screens and print messages to users in a beautiful way!
Below are few examples of figlet in quick run :
figlet utility examples
toilet tool
I know its funny name. Yeah but it’s a tool which do exist in Linux! Check if the toilet package is installed or not and install it if required. Once installed you can submit text to toilet command.
cmatrix: One of the command to have fun in a Linux terminal. It will turn your terminal into the Hollywood movie “MATRIX” like a cool desktop.
Hollywood movie MATRIX falling code in Linux terminal
About cmatrix program:
It’s written by Chris Allegretta. The Cmatrix page can be found here. This program is distributed via the GNU GPL and its Sourceforge page is here. To download the latest release visit Sourceforge page.
Have you seen the Hollywood movie “Matrix”? You must have liked those monitors with falling green code. It looks like a cool hacker/coder desktop! After the movie went to the box office, many matrix screensavers were out for windows. Do you want one for Linux? Like the one below?
Matrix falling code in terminal
Yes, that’s possible. You can have such a matrix-like desktop in Linux terminal too. In very simple two steps.
If you don’t have a YUM repository configured then you can download a standalone file (check Sourceforge page if this link is broken). Then follow below commands to set it up from source code.
Download above mentioned file, un-zip, un-tar it and goto unpacked directory cmatrix-1.2a
Within cmatrix directory execute below commands.
# aclocal
aclocal: warning: autoconf input should be named 'configure.ac', not 'configure.in'
# autoconf
# automake -a
automake: warning: autoconf input should be named 'configure.ac', not 'configure.in'
configure.in:3: warning: AM_INIT_AUTOMAKE: two- and three-arguments forms are deprecated. For more info, see:
configure.in:3: http://www.gnu.org/software/automake/manual/automake.html#Modernize-AM_005fINIT_005fAUTOMAKE-invocation
Makefile.am: installing './depcomp'
automake: warning: autoconf input should be named 'configure.ac', not 'configure.in'
Then configure and make ready to install.
# ./configure
checking for a BSD-compatible install... /bin/install -c
checking whether build environment is sane... yes
/root/cmatrix-1.2a/missing: Unknown `--is-lightweight' option
Try `/root/cmatrix-1.2a/missing --help' for more information
configure: WARNING: 'missing' script is too old or missing
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking for gcc... gcc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ISO C89... none needed
checking for style of include used by make... GNU
checking dependency style of gcc... gcc3
checking whether make sets $(MAKE)... (cached) yes
checking for main in -lncurses... yes
checking how to run the C preprocessor... gcc -E
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking fcntl.h usability... yes
checking fcntl.h presence... yes
checking for fcntl.h... yes
checking sys/ioctl.h usability... yes
checking sys/ioctl.h presence... yes
checking for sys/ioctl.h... yes
checking for unistd.h... (cached) yes
checking termios.h usability... yes
checking termios.h presence... yes
checking for termios.h... yes
checking termio.h usability... yes
checking termio.h presence... yes
checking for termio.h... yes
checking return type of signal handlers... void
checking for putenv... yes
checking curses.h usability... yes
checking curses.h presence... yes
checking for curses.h... yes
checking ncurses.h usability... yes
checking ncurses.h presence... yes
checking for ncurses.h... yes
checking for tgetent in -lncurses... yes
"Using ncurses as the termcap library"
checking for use_default_colors in -lncurses... yes
checking for resizeterm in -lncurses... yes
checking for wresize in -lncurses... yes
checking for consolechars... no
checking for setfont... /bin/setfont
checking for /usr/lib/kbd/consolefonts... yes
checking for /usr/share/consolefonts... no
checking for mkfontdir... no
checking for /usr/lib/X11/fonts/misc... no
checking for /usr/X11R6/lib/X11/fonts/misc... no
configure: WARNING:
*** You do not appear to have an X window fonts directory in the standard
*** locations (/usr/lib/X11/fonts/misc or /usr/X11R6/lib/X11/fonts/misc). The
*** mtx.pcf font will not be installed. This means you will probably not
*** be able to use the mtx fonts in your x terminals, and hence be unable
*** to use the -x command line switch. Sorry about that...
checking that generated files are newer than configure... done
configure: creating ./config.status
config.status: creating Makefile
config.status: creating cmatrix.spec
config.status: creating config.h
config.status: executing depfiles commands
# make
(CDPATH="${ZSH_VERSION+.}:" && cd . && autoheader)
autoheader: WARNING: Using auxiliary files such as `acconfig.h', `config.h.bot'
autoheader: WARNING: and `config.h.top', to define templates for `config.h.in'
autoheader: WARNING: is deprecated and discouraged.
autoheader:
autoheader: WARNING: Using the third argument of `AC_DEFINE' and
autoheader: WARNING: `AC_DEFINE_UNQUOTED' allows one to define a template without
autoheader: WARNING: `acconfig.h':
autoheader:
autoheader: WARNING: AC_DEFINE([NEED_FUNC_MAIN], 1,
autoheader: [Define if a function `main' is needed.])
autoheader:
autoheader: WARNING: More sophisticated templates can also be produced, see the
autoheader: WARNING: documentation.
rm -f stamp-h1
touch config.h.in
cd . && /bin/sh ./config.status config.h
config.status: creating config.h
make all-am
make[1]: Entering directory `/root/cmatrix-1.2a'
gcc -g -O2 -o cmatrix cmatrix.o -lncurses -lncurses
make[1]: Leaving directory `/root/cmatrix-1.2a'
Type cmatrixcommand and experience matrix! You can exit out the matrix screen anytime by hitting ctlr+c on the terminal. Check cmatrix command in action in the GIF above!
Reader’s tip :
One of our readers, @Pranit Raje sent us this one-liner which did the trick. Its not as exact matrix code as we saw above but yeah it’s promising. Try and have fun in the terminal.
This article will help you understand the package naming convention followed while naming RPM or DEB packages. It helps while you work on package management.
Package naming convention
Linux world is moved by packages since you need a flavor punch on plain vanilla OS! Although there are quite a few package managers available in the market largely two package managers are popular: RPM (Red Hat package manager) & DEB (Debian package manager).
Red Hat package managers release their packages with extension .rpm while Debian package managers have .deb extension. The extension really doesn’t matter in Linux world but still, it’s there for identification purposes for humans!
Apart from extensions they also have a package naming convention which makes it easy to identify package name, version, release & what architecture it supports. Lets quickly walk through these conventions.
Red Hat package naming convention
Red Hat package name follows below format –
packagename-version-release.architecture.rpm
Field involved here are
It starts with the package name
Then its version (separated by hyphen – from the last field)
Then its release (separated by hyphen – from the last field)
Sometimes OS details are padded here (separated by a dot . from the last field)
Then architecture for which package built (separated by a dot . from the last field)
Ends with rpm extension (separated by a dot . from the last field)
For example, look at this telnet package file name “telnet-0.17-60.el7.x86_64.rpm“
Here,
telnet is a package name
0.17 is version
60 is release
el7 is enterprise Linux 7 (package built for rhel7)
x86_64 is architecture
Extra OS details mentioned in names can be :
elX or rhlX – RHEL X
suseXXY – Suse Linux XX.Y
fcX – Fedora Core X
mdv or mdk – Mandriva Linux
Debian package naming convention
Debian package name follows below format –
packagename_version-release_architecture.deb
Field involved here are
It starts with the package name
Then its version (separated by underscore – from the last field)
Then its release (separated by a hyphen – from the last field)
Sometimes Debian codename details are padded here (separated by hyphen – from the last field)
Then architecture for which package built (separated by a dot . from the last field)
Ends with deb extension (separated by a dot . from the last field)
Debian codename can be squeeze or wheezy.
For example look at this telnet package file name “telnet_0.17-40_amd64.deb“
Here,
telnet is a package name
0.17 is version
40 is release
amd64 is architecture
Different types of architectures which can be seen in names are :
x86_64 or amd64 – 64 bit on x86 microprocessor
i386 – The Intel x86 family of microprocessors, starting with the 80386.
ppc – The Power PC microprocessor family.
alpha – The Digital Alpha microprocessor family.
sparc – Sun Microsystem SPARC processor family.
noarch – No particular architecture. The package may work on all types of architecture.
We will be seeing how to uninstall packages from YUM and APT based Linux systems. Package removal also knows as an erasing package from the system.
Package removal on YUM based system
Removing package using yum
On YUM based system like Red Hat or CentOS, the package can be removed by supplying erase or remove argument to yum command along with package name. For example to remove telnet, we will use yum remove telnet
# yum remove telnet
Loaded plugins: amazon-id, rhui-lb, search-disabled-repos
Resolving Dependencies
--> Running transaction check
---> Package telnet.x86_64 1:0.17-60.el7 will be erased
--> Finished Dependency Resolution
Dependencies Resolved
=============================================================================================================================================================
Package Arch Version Repository Size
=============================================================================================================================================================
Removing:
telnet x86_64 1:0.17-60.el7 @rhui-REGION-rhel-server-releases 113 k
Transaction Summary
=============================================================================================================================================================
Remove 1 Package
Installed size: 113 k
Is this ok [y/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Erasing : 1:telnet-0.17-60.el7.x86_64 1/1
Verifying : 1:telnet-0.17-60.el7.x86_64 1/1
Removed:
telnet.x86_64 1:0.17-60.el7
Complete!
The above output will be the same even if you use yum erase telnetcommand. Before removing it will print package details to be removed on screen and ask for confirmation to avoid unwanted removals.
Removing package using rpm command
Same task can be achieved by using rpm command with erase -e option.
In above example we used -e (erase), -v (verbose) and -h (print hash marks) along with name of package.
Package removal on APT based system
Removing package using apt-get
On APT based systems like Ubuntu or Debian, the package can be removed with apt-get remove <package_name> command. Note that like YUM this command doesn’t support erase option.
# apt-get remove telnet
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
telnet
0 upgraded, 0 newly installed, 1 to remove and 60 not upgraded.
After this operation, 182 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 81678 files and directories currently installed.)
Removing telnet (0.17-40) ...
Processing triggers for man-db (2.7.5-1) ...
apt-get to asks for confirmation before removing package from system.
Removing package using dpkg
With Debian package manager command i.e. dpkg, this can be done using --remove argument.
# dpkg --remove telnet
(Reading database ... 81678 files and directories currently installed.)
Removing telnet (0.17-40) ...
Processing triggers for man-db (2.7.5-1) ...
See above output as it removes telnet.
Observe that dpkg or rpm commands don’t ask for user confirmation before removing the package.
