loganalyzer | Adiscon LogAnalyzer , a web frontend

You should replace the RandomAccessFileAppender with a simple FileAppender.

Your issue is not caused by the use of asynchronous loggers, but by the appender you use:

• Java's RandomAccessFile, which is used by the RandomAccessFileAppender opens files in read/write mode without the O_APPEND option (cf. open(2)),
• FileOutputStream, which is used by the usual FileAppender, opens files in write only mode with the O_APPEND option.

The presence or the absence of this option influences how writes are performed:

O_APPEND The file is opened in append mode. Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). The modification of the file offset and the write operation are performed as a single atomic step.

(from man open(2)).

When you truncate your log file a FileAppenders offset will be reset to 0, while a RandomAccessFileAppender will continue writing at the previous position.

Remark: Log4j also provides a RollingFileAppender, which will remove the need to use logrotate at all.

Edit: the exact options used to create the objects used by the managers can be found:

• for the FileManager in FileManagerFactory#createManager,
• for the RandomAccessFileManager in RandomAccessFileManagerFactory#createManager.