摘要：either '$(foo)' or '${foo}' is a valid reference to the variable foo. This special significance of '$' is why you must write '$$' to have the effect o 阅读全文

摘要：The /var/log/wtmp file records all logins and logouts. The /var/log/lastlog file records when each user last logged in. The /var/log/faillog file reco 阅读全文