The cause is that the backup script of scp on a server crontab fails to be run at regular intervals. It is okay to manually execute the script. Therefore, you need to find the cause from the crontab log, suddenly I found no cron logs under my/var/log. Here I will record how ubuntu server can view the crontab log www.2cto.com crontab record log to modify rsyslog [html] sudo vim/etc/rsyslog. d/50-default.conf [html] cron. */var/log/cron. log # Remove the comment in front of cron and restart rsyslog www.2cto.com [html] sudo service rsyslog restart to view crontab log [html] less/var/log/cron. log crontab problem locating view log/var/log/cron. log and/var/mail/$ user because the crontab running log is recorded in cron. log. When sendmail is enabled, the system will send an email www.2cto.com ssh error message to the current crontab running owner to delete the current host user. ssh/hosts file