How to determine whether to install jdk in linux

How to check whether jdk is installed in Linux:

1. Check whether the jdk environment variable is set: echo $JAVA_HOME;

2. Run the command: java -verion to see if you can check the version. If you can, just run it;

3. Check the background process: ps -ef|grep java.

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linux directory structure:

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/bin is used to store user commands. /usr/bin is also used to store user commands.

/sbin The storage location of many system commands (such as shutdown). /usr/sbin also contains many system commands.

/root The home directory of the root user (superuser).

/mnt This directory usually contains the mount point of the file system that is mounted after the system boots. For example, the default CD mount point is /mnt/cdrom/. You can create a mount point for the U disk: mkdir /mnt/usb.

/boot includes the kernel and other files used during system startup, with a maximum size of no more than 200M. Usually I create a primary partition of 1G for /boot.

/lost found is used by fsck to place scattered files (files without names).

/lib contains many library files used by programs in /bin and /sbin. The directory /usr/lib contains further library files for user programs. The /lib directory contains the library files required by the programs in the /bin and /sbin directories. To put it simply, /lib is at the kernel level; /usr/lib is at the system level; /usr/local/lib is at the user level. Shared libraries used only by programs in the /usr directory do not need to be placed in the /lib directory. Only the libraries required by programs under /bin and /sbin must be placed in the /lib directory.

/dev stores device files.

/etc contains many configuration files and directories.

/var is used to store variable (or changing) files, such as log files, printer spool files, virtual machine image files, etc.

/usr includes files and directories directly related to system users, such as applications and the library files that support them.

/proc A virtual file system (not actually stored on the disk), which contains system information used by certain programs.

/initrd is the directory used to mount the initrd.img image file when the computer starts and to load the required device modules. Do not delete the /initrd directory. If you delete this directory and then reboot Red Hat Linux, you will not be able to boot your computer.

/tmp Temporary directory for users and programs.

/tmp gives all system users read and write rights.

/home The default location of the user's home directory.

/opt The storage directory for optional files and programs. This directory is primarily used by third-party developers to easily install and uninstall their packages.

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