How to change the interface name in CentOS/RHEL 8 using prefixdevname
This post will help to change the network interface name using prefixdevname utility in CentOS/RHEL 8 systems. Installation and configuration 1. Install the required package using dnf utility: # dnf...
View ArticleDocker Basics – Expose ports, port binding and docker link
This post illustrates three methods to link Docker containers. Expose ports and port binding Expose ports This method is used for within the same network or the docker host. Containers on the same...
View Article‘docker images’ command error – “Permission Denied”
The Problem A regular user is not able list images using docker images command. Following error can be observed. user01> docker images Got permission denied while trying to connect to the Docker...
View ArticleUnderstanding “docker stats” Command Output
Question: How to monitor a running docker container performance metrics. For example, CPU,memory, I/O and network stats? The docker stats command can continuously report the basic CPU, memory, network...
View ArticleHow to find docker storage device and its size (device mapper storage driver)
Question: How to find the running docker storage device when docker is using the device-mapper storage driver and then check the size of it? 1. Please run the “docker info” command to display docker...
View ArticleHow to Pause and Resume Docker Containers
Question: How to Pause and Resume running containers on docker host? This post will help to know about pausing and resuming any running containers on the Docker host. Let’s first start the docker...
View Article[Webinar] DMARC Analyzer technical deep-dive webinar
Attend our free webinar on Dec 11th to learn more about our app and how DMARC can help in eliminating spam and phishing attacks that are spoofing your brand. Limited spots available, save your seat...
View Article“su: Authentication failure” – in Docker
The Problem In some situations, a normal user within a Docker container cannot run ‘su’ command to switch user. When ‘su’ command is issued, the following error returns. $ su – Password: [entering...
View ArticleHow to change the default IP address of docker bridge
Question: what is the proper procedure to reconfigure the docker interface to use an address range (e.g., > 172.200) for the virtual interfaces it uses? You can reconfigure the default bridge...
View ArticleHow to Configure Network Namespaces in Docker Containers
This post tells how Docker uses network namespace to isolate resources. The following figure is the lab setup to help you understand the steps visually: 1. Create two network namespaces: ns1 and ns2. –...
View Articlelvremove failing to remove volume after using ‘shred’ command
The Problem When trying to delete volume group by using lvremove, vgremove, pvremove command after executing shred command for physical volume as shown below, fails repeatedly. # shred -vfz -n 3...
View ArticleMySQL – How to undo (rollback) a set of SQL statements
What is Conducting a Transaction? If you have a series of SQL statements that you want to run which involve adding, deleting, or changing data contained in InnoDB or BDB tables, but want to be sure...
View Articlerpm: error while loading shared libraries: invalid ELF header
The Problem rpm commands issue the following error: rpm: error while loading shared libraries: /usr/lib64/liblzma.so.0: invalid ELF header The Solution In this instance, either liblzma.so or the link...
View ArticleUnable to login with GUI on CentOS/RHEL 7
The Problem can’t login to the system via GUI On CentOS/RHEL 7. Also, gdm segfault with below error after which unable to login to GUI. kernel: gdm-simple-slav[4172]: segfault at 0 ip 00007f93d911c7df...
View ArticleWhat are “segfault” messages in /var/log/messages file
This post explains how to analyse the segfault message in message file and to identify the problem in application or operating system side. What is “segfault”? A segmentation fault (often shortened to...
View ArticleHow to add additional language support in CentOS/RHEL
Question: How to add additional language support in CentOS/RHEL? To add specific language support in CentOS/RHEL, you need firstly confirm the correct language group name by “yum grouplist” command. #...
View ArticleHow to enable core dump for Applications on CentOS/RHEL
1. In CentOS/RHEL core file creation is disabled by default. To enable it, executing the below command: # ulimit -S -c unlimited > /dev/null 2>&1 then execute the program in the same shell...
View ArticleCentOS/RHEL 6 Kernel Panic – “Out of memory” kernel parameter panic_on_oom is...
The Problem CentOS/RHEL 6 system reboot due too out of memory error: DUMPFILE: vmcore [PARTIAL DUMP] CPUS: 2 DATE: Mon Feb 29 05:28:02 2016 UPTIME: 33 days, 09:45:55 LOAD AVERAGE: 1.88, 1.52, 1.41...
View ArticleCentOS/RHEL – How to Remove stale ISCSI Target Node Information from ISCSI...
The Problem Stale ISCSI target connections which are still present on Initiator node can lead to various issues like: 1. hung iscsid service which can lead to global outage. 2. flood of messages error...
View ArticleUnderstanding mysqlcheck and myisamchk utilities
mysqlcheck Client Program In some cases, mysqlcheck is more convenient than issuing SQL statements directly. For example, if you provide it with a database name as its argument, mysqlcheck determines...
View ArticleMySQL Table Maintenance – InnoDB, MyISAM, MEMORY, ARCHIVE
InnoDB Table Maintenance If a table check indicates problems, restore the table to a consistent state by dumping it with mysqldump, dropping it, and re-creating it from the dump file. In the event of a...
View ArticleOracle SQL Script to Detect Tablespace Fragmentation
The following is a script that will determine how many extents of contiguous free space you have in Oracle as well as the total amount of free space you have in each tablespace. From these results, you...
View ArticleHow to configure Linux Resource Groups (cgroups) for MySQL
The following provides the procedure for configuring and using resource groups under Linux: 1. To use cgroups, you must install the “libcgroup” package on your system. # yum install libcgroup 2. Create...
View ArticleFailed to Download Metadata for Repo ‘repo_name’
The Problem All the dnf commands fail with the following error: # dnf repolist Oracle Linux 8 BaseOS Latest (x86_64) 0.0 B/s | 0 B 00:00 Failed to download metadata for repo ‘ol8_baseos_latest’ Error:...
View ArticleOracle – How To Check if Autoextensible Datafiles Set To Maxsize Unlimited
Question: How to check whether the datafiles are set to AUTOEXTEND and UNLIMITED? We can query the DBA_DATA_FILES view to check whether the data file is in AUTOEXTEND mode. SQL> select...
View ArticleHow to Disable AUTOEXTEND Mode on a datafile in Oracle Database
Question: How do you take a datafile out of autoextend mode? Oracle datafiles were given the ability to extend automatically if needed from a long time. If the given datafile is unable to allocate the...
View ArticleHow to Rebuild GRUB on MSDOS Partition Type in CentOS/RHEL/OEL 7
Question: How to Rebuild Grub on Linux servers with MSDOS Partition type. (proc) (hd0) (hd0,msdos5) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1) 1. Execute the following commands in Grub prompt to set the...
View ArticleCounting Rows Of A Table In MySQL Server
Let’s understand what are the available options to get an accurate number or an estimation of rows in a MySQL table. The option to get an accurate count of rows in a table is to perform: SELECT...
View ArticleHow To Shrink A Temporary Tablespace in Oracle Database
Question: How to resize the TEMPFILE(s) for a temporary tablespace after they have grown larger than needed? Large sort operations can cause temporary tablespaces to grow very large and as such there...
View ArticleHow to Compress and Decompress .bz2 files in Linux Using bzip2 Command
Introduction In this article we are going to learn How to compress files using bz2 file compression tool (bzip2 linux command) and unzip bz2 compressed file. bzip2 is a open source compress tool...
View ArticleHow to shrink a Temporary Tablespace datafile in Oracle
The database has a program which performs a huge sort operation (e.g. end of the year reporting process). This may cause the TEMP tablespace to grow and occupy most of the space on the file system. In...
View ArticleDowngrading an rpm package to a lower version (using “rpm” command)
Question: How to downgrade an rpm package in CentOS/RHEL 6 system to a lower version using the “rpm” command? Its not really recommended to use rpm command instead of yum to downgrade an rpm package....
View ArticleWhat are Bash Exit Codes in Linux
What is an exit code Every script, command, or binary exits with a return code. You can see this value in the special variable $?. Return codes are numeric and are limited to being between 0-255...
View ArticleWhat is the difference between & (ampersand) and && (double ampersand) while...
To run more that one command simultaneously we can use the & (ampersand) special character. Another use of & is running the commands in the background. In that case though, you should use &...
View ArticleHow to allow ssh with empty passwords in Linux
Question: How can we allow a user with empty password to login to a Linux system? Although it seems a risky requirement, but sometimes in a private, development environment this can come handy. Also...
View ArticleHow to Configure SSH to restrict Users/Groups with allow and deny directives
Question: How can we restrict user/group access to a system using ssh? SSH uses specific files for configuration to achieve these various restrictions. Inbound ssh sessions (into the host) are handled...
View ArticleHow to Set Space limits for MySQL for database/schema/table
MySQL itself has not such quotas, but it is possible to partially manage quota limitation at engine level. For MyISAM it is possible to limit table size using option myisam_data_pointer_size This...
View ArticleHow to test a PHP script
PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. PHP runs on all major operating systems, from Unix variants...
View ArticleHow to check and repair ACFS with FSCK
The Problem You noticed many inconsistencies in different asm metadata views, asmcmd and os outputs that are associated with the ACFS file system. Database shows corruption in RMAN or from dbverify....
View ArticleHow to Install an Configure MASTER PDF EDITOR IN UBUNTU
Introduction In this article we are going to learn How to install master PDF editor in Ubuntu 16.04. master PDF editor is a open source free PDF editor application for Linux. It’s a light weight and...
View ArticleLinux “seq” Command Examples
The seq command prints a sequence of integers or real numbers, suitable for piping to other programs. The seq command can come in handy in various other commands and loops to generate sequence of...
View ArticleHow to Configure 2-way replication in an existing Master, Slave MySQL...
This post applies both to Server and Cluster environments, as cluster replication uses the MySQL Server / API node to facilitate the replication. There are minor config differences between the two...
View ArticleHow to Backup a MySQL Cluster
Basics There are two common options for backing up a MySQL cluster database: mysqldump or a native cluster backup. The utility mysqldump is more general since it is a storage engine independent. It has...
View ArticleMimecast Announces Acquisition of DMARC Analyzer
Acquisition Offers Powerful Brand Protection With Stronger Blocking Of Spoofing Attacks Lexington, MA – November 14, 2019 – Mimecast Limited (NASDAQ: MIME), a leading email and data security company,...
View ArticleMimecast Announces Acquisition of DMARC Analyzer
Acquisition Offers Powerful Brand Protection With Stronger Blocking Of Spoofing Attacks Lexington, MA – November 14, 2019 – Mimecast Limited (NASDAQ: MIME), a leading email and data security company,...
View ArticleMimecast Announces Acquisition of DMARC Analyzer
Acquisition Offers Powerful Brand Protection With Stronger Blocking Of Spoofing Attacks Lexington, MA – November 14, 2019 – Mimecast Limited (NASDAQ: MIME), a leading email and data security company,...
View ArticleUse SPF Compression if you have to many DNS lookups
DMARC Analyzer offers managed SPF compression. SPF compression complements a DMARC project. SPF compression enables a safe, smart and fast way to reach the DMARC reject policy. SPF compression is...
View ArticleUse SPF Compression if you have to many DNS lookups
DMARC Analyzer offers managed SPF compression. SPF compression complements a DMARC project. SPF compression enables a safe, smart and fast way to reach the DMARC reject policy. SPF compression is...
View ArticleUse SPF Compression if you have to many DNS lookups
DMARC Analyzer offers managed SPF compression. SPF compression complements a DMARC project. SPF compression enables a safe, smart and fast way to reach the DMARC reject policy. SPF compression is...
View ArticleUse SPF Compression if you have to many DNS lookups
DMARC Analyzer offers managed SPF compression. SPF compression complements a DMARC project. SPF compression enables a safe, smart and fast way to reach the DMARC reject policy. SPF compression is...
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