FTP error, unable to establish data connection; 425 Failed to establish connection.

problem description

normal connection, can operate, occasionally occur this problem?

so far, I haven"t found out what"s going on, even if it"s changed to active PORT. 

227 Entering Passive Mode (xxx,xxx,xxx,xx,156,81)

I want to know what the whole () stands for

.
Ftp vsftpd
Apr.01,2021

the port number used by ftp server.
256 / 156 / 81

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-42995c9-595a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-42995c9-595a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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