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 including Linux, FreeBSD, Ubuntu, Debian, and Solaris to Windows and Mac OS X. It can be used with all leading web servers, including Apache, Nginx, OpenBSD servers to name a few; even cloud environments like Azure and Amazon are on the rise. Below are some of the ways in which a PHP script can be … [Read more...] about How to test a PHP script
How 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 variable limits default data pointer size: less this variable is, less rows would be allowed to be saved in the table. "Table is full" error will be reported if this option is considered. For InnoDB it is possible to specify hard limit of shared tablespace: syntax is similar to … [Read more...] about How to Set Space limits for MySQL for database/schema/table
How 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 by sshd (the ssh daemon). This process has its own configuration file, /etc/ssh/sshd_config. The parameters in the /etc/ssh/sshd_config file that apply are AllowGroups, AllowUsers, DenyGroups, and DenyUsers. If these parameters are set, it will affect all users from all hosts. To restrict … [Read more...] about How to Configure SSH to restrict Users/Groups with allow and deny directives
How 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 openssh provides you with an option to have empty passwords for users while doing ssh. From the man page of sshd_config: # man sshd_config ... PermitEmptyPasswords When password authentication is allowed, it specifies whether the server allows login to accounts with empty … [Read more...] about How to allow ssh with empty passwords in Linux
What is the difference between & (ampersand) and && (double ampersand) while executing simultaneous commands on Linux
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 & once and the end of the command or script. For example: # [some command or script] & Using & (ampersand) to run commands simultaneously In order to run 2 commands simultaneously use the & special character between the 2 or more commands. The syntax is: # command1 & command2 & command3 .. For example, … [Read more...] about What is the difference between & (ampersand) and && (double ampersand) while executing simultaneous commands on Linux
What 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 because an unsigned 8-bit integer is used. If you use a value of -1, it will return 255. Each execution terminates with an exit code, whether successful or not, with an error message or silently. For example: $ date ; echo $? Sat Jan 18 08:06:07 IST 2020 0 As you can see, the exit code is 0 … [Read more...] about What are Bash Exit Codes in Linux
Downgrading 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. But in case if you don't have a choice use the below procedure. Pre-requisites Make sure you have downloaded all the packages and its dependencies for the lower version. Downgrading rpm version For the purpose of this post we are downgrading the systemd packages from … [Read more...] about Downgrading an rpm package to a lower version (using “rpm” command)
How 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 this example, the report process may run once or twice a year and there is no need to maintain/keep a huge tempfile. The TEMP tablespace was created with datafiles (dictionary managed tablespace temporary) as AUTOEXTEND ON MAXSIZE UNLIMITED to avoid the Error: ORA-1652 Text: unable to extend temp … [Read more...] about How to shrink a Temporary Tablespace datafile in Oracle
How 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 similar to zip & gzip compression tool used to compress large sized files to reduce it’s size. bzip2 can compress files not directories. bzip2 gives more compression as compared to gzip and zip. bzip2 Linux command was developed by Julian Seward on year 1996 and released under BSD style license. Why … [Read more...] about How to Compress and Decompress .bz2 files in Linux Using bzip2 Command
How 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 may be a need to 'downsize' after such operations. Until Oracle 11g there was no SQL command to release the unused allocated temporary space. One workaround for this problem is to create a new empty temporary tablespace with a smaller size, assign this new tablespace to the users and then drop … [Read more...] about How To Shrink A Temporary Tablespace in Oracle Database