abrtd 自动上报bug的工具
-f file
True if file exists and is a regular file.
atd 定时运行命令的工具
-x file
True if file exists and is executable.
auditd 审计功能
audit系统构成了linux安全防护的根本,想看代码的可以访问https://fedorahosted.org/audit/browser
-z string
True if the length of string is zero.