SELinux (Security Enhanced Linux ) is a Linux kernel security module that allows administrators and users more control over access controls. It allows access based on SELinux policy rules.

SELinux policy rules specify how processes and users interact with each other as well as how processes and users interact with files.

When no SELinux policy rule explicitly allows access, such as for a process opening a file, access is denied.

SELinux has three modes:

  • Enforcing: SELinux allows access based on SELinux policy rules.
  • Permissive: SELinux only logs actions that would have been denied if running in enforcing mode.
  • Disabled: No SELinux policy is loaded.

By default, in CentOS 7, SELinux is enabled and in enforcing mode.

It is recommended to keep SELinux in enforcing mode, but in some cases, you may need to set it to a permissive mode or disable it completely.

In this tutorial, we will show you how to disable SELinux on CentOS 7 systems.

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2.MD5 Using MessageDigest Class class:

MessageDigest.getInstance(String Algorithm)
public void update(byte [] input)
public byte[] digest()

generates a hash for a password and then verifies it:

public void givenPassword_whenHashing_thenVerifying() 
  throws NoSuchAlgorithmException {
    String hash = "35454B055CC325EA1AF2126E27707052";
    String password = "ILoveJava";
    MessageDigest md = MessageDigest.getInstance("MD5");
    byte[] digest = md.digest();
    String myHash = DatatypeConverter

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删除表A的记录时,Oracle 报错:“ORA-02292:违反完整约束条件(XXX.FKXXX)- 已找到子记录


select a.constraint_name, a.table_name, b.constraint_name
from user_constraints a, user_constraints b
where a.constraint_type = 'R'
and b.constraint_type = 'P'
and a.r_constraint_name = b.constraint_name
and a.constraint_name = 'FKXXX'



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