这意味着该文件有一个SELinux上下文。使用ls -Z查看实际的SElinux上下文值。它在GNU Coreutils的“info”文件中有说明：列出了哪些信息。
相关引述：

Following the file mode bits is a single character that specifies
 whether an alternate access method such as an access control list
 applies to the file.  When the character following the file mode
 bits is a space, there is no alternate access method.  When it is a
 printing character, then there is such a method.

 GNU ‘ls’ uses a ‘.’ character to indicate a file with a security
 context, but no other alternate access method.

 A file with any other combination of alternate access methods is
 marked with a ‘+’ character.

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