它指定要触发轮换的 日志文件 的大小。例如，size 50M一旦文件大小为50MB或更大，将触发日志轮换。您可以将后缀M用于兆字节，k千字节和G千兆字节。如果不使用后缀，则将其表示为字节。您可以在最后检查示例。有三个指令可用size，maxsize和minsize。根据手册页：

minsize size
              Log  files  are  rotated when they grow bigger than size bytes,
              but not before the additionally specified time interval (daily,
              weekly,  monthly, or yearly).  The related size option is simi-
              lar except that it is mutually exclusive with the time interval
              options,  and  it causes log files to be rotated without regard
              for the last rotation time.  When minsize  is  used,  both  the
              size and timestamp of a log file are considered.

size size
              Log files are rotated only if they grow bigger then size bytes.
              If size is followed by k, the size is assumed to  be  in  kilo-
              bytes.  If the M is used, the size is in megabytes, and if G is
              used, the size is in gigabytes. So size 100,  size  100k,  size
              100M and size 100G are all valid.
maxsize size
              Log files are rotated when they grow bigger than size bytes even before
              the additionally specified time interval (daily, weekly, monthly, 
              or yearly).  The related size option is  similar  except  that  it 
              is mutually exclusive with the time interval options, and it causes
              log files to be rotated without regard for the last rotation time.  
              When maxsize is used, both the size and timestamp of a log file are                  
              considered.

这是一个例子：

"/var/log/httpd/access.log" /var/log/httpd/error.log {
           rotate 5
           mail www@my.org
           size 100k
           sharedscripts
           postrotate
               /usr/bin/killall -HUP httpd
           endscript
       }

这是文件/var/log/httpd/access.log和的说明/var/log/httpd/error.log。每当大小超过100k时，它们都会旋转一次，并且www@my.org经过5次旋转后会将旧日志文件邮寄（未压缩）到，而不是将其删除。这sharedscripts意味着该postrotate脚本将只运行一次（在压缩旧日志之后），而不是为每个循环日志运行一次。请注意，在本节的开头，第一个文件名周围的双引号允许logrotate旋转名称中带有空格的日志。会使用普通的shell引用规则，并带有,和\字符。