# Fault Diagnosis and Analysis## Error LogWhen JuiceFS run in background (through [`-d` option](command_reference.md#juicefs-mount) when mount volume), logs will output to syslog. Depending on your operating system, you can get the logs through different commands:```bash# macOS$ syslog | grep'juicefs'# Linux$ cat /var/log/syslog | grep'juicefs'```There are 4 log levels. You can use the `grep` command to filter different levels of logs for performance analysis or troubleshooting:```$ cat /var/log/syslog | grep 'juicefs' | grep '<INFO>'$ cat /var/log/syslog | grep 'juicefs' | grep '<WARNING>'$ cat /var/log/syslog | grep 'juicefs' | grep '<ERROR>'$ cat /var/log/syslog | grep 'juicefs' | grep '<FATAL>'```## Access LogThere is a virtual file called `.accesslog` in the root of JuiceFS to show all the operations and the time they takes, for example:```bash$ cat /jfs/.accesslog2021.01.15 08:26:11.003330 [uid:0,gid:0,pid:4403] write (17669,8666,4993160): OK <0.000010>2021.01.15 08:26:11.003473 [uid:0,gid:0,pid:4403] write (17675,198,997439): OK <0.000014>2021.01.15 08:26:11.003616 [uid:0,gid:0,pid:4403] write (17666,390,951582): OK <0.000006>```The last number on each line is the time (in seconds) current operation takes. You can use this to debug and analyze performance issues.