db2diag命令，是用来查看db2数据库运行日志信息的，实际上，db2运行日志是记录在db2diag.log文件中，可以 通过此文件，查看记录的有关DB2数据库详细的错误信息，而db2diag只是查看该日志文件的一个小工具而已。db2数据库在运行过程中如果经常有报错的话，这个文件增长的会很快，需要定期清理，备份移走或者删除，通常有两种方法：

可以通过执行db2 get dbm cfg 来查看Diagnostic data directory path(DIAGPATH) 参数的设置。

1、使用db2diag工具，直接执行命令db2diag -A /db2diagbak (备份至/db2diagbak ,使用db2diag -h查看db2diag帮助)，系统会自动移走db2diag.log并将备份的文件名添加上当前日期时间信息。

2、直接备份，在db2停止运行的情况下，将db2diag.log文件备份至其他文件系统，该文件删除后在db2启动后会自动重建。

附录：

$db2diag -h

db2diag - The db2diag.log Analysis Tool

db2diag is a tool for filtering and formatting the db2diag.log file

Command syntax:
                   .------------.  .--------------.
                   V            |  V              |
      >>--db2diag--+------------+--+--------------+--><
                    |          |    |            |
                     --option--      --filename--

Command parameters:

filename          - one or more space-separated path names of diagnostic logs
 -help   , -h , ?  - help information. To get help on help, try "db2diag -h h"
 -filter , -g      - case-sensitive search for a list of field-pattern pairs
 -gi               - case-insensitive search for a list of field-pattern pairs
 -gv               - case-sensitive invert matching
 -gvi    , -giv    - case-insensitive invert matching
 -invert , -v      - invert the sense of matching for all filtering options
 -exist            - record field must exist in order to be processed
 -pid              - find all records for a list of process IDs
 -tid              - find all records for a list of thread IDs
 -eduid            - find all records for a list of EDU IDs
 -node   , -n      - find all records for a list of nodes
 -error  , -e      - find all records for a list of errors
 -level  , -l      - find all records for a list of severity levels
 -history, -H      - display the history of logged records for a time interval
 -time   , -t      - display all the records within a particular time interval
 -count  , -c      - display a count of matching records
 -verbose, -V      - display all record fields whether they contain data or not
 -strict           - display records using one "field: value" pair per line
 -cbe              - display records in the Common Base Event (CBE) format
 -fmt              - format tool's output using a format string
 -output , -o      - save output into a file
 -follow , -f      - continuously display appended records as the file grows
 -archive, -A      - archive a diagnostic log file
 -readfile         - read from a file ignoring terminal input (used in scripts)
 -rc               - display descriptions of DB2 error return codes, ZRC or ECF
 -ecfid            - display function info extracted from the numeric ECF ID
 -facility, -fac   - display messages from a particular facility

"db2diag -h <option1[,option2[,option3...]]>" - displays additional help and
  usage examples for one or more options specified in the options list

"db2diag -h brief"    - displays help for all options without examples

"db2diag -h examples" - displays a few typical examples to get started

"db2diag -h tutorial" - displays more advanced examples covering all features

"db2diag -h notes"    - displays usage notes and restrictions that apply

"db2diag -h all"      - displays help in the most complete form with detailed
                         information about all options and usage examples