Ignore "nohup" warning not working for mysqldump

Question

I know there're tons similar question but somehow I can't get it right.

When run this command, my "dump.sql" produced desired result

mysqldump -uuser -ppassword --comments --single-transaction --quick mydb desired_table | gzip >dump.sql.gz

This is the first line of dump.sql

-- MySQL dump 10.13  Distrib 8.0.21, for Linux (x86_64)

But with this command:

nohup mysqldump -uuser -ppassword --comments --single-transaction --quick mydb desired_table | gzip >dump.sql.gz 2>/dev/null &

This is the first line of dump.sql:

mysqldump: [Warning] Using a password on the command line interface can be insecure.

Which will cause error when import the dump file. How? From what I understand, "2>" means redirect error. If I change to this command, nothing in the "dump.log":

nohup mysqldump -uuser -ppassword --comments --single-transaction --quick mydb desired_table | gzip >dump.sql.gz 2>dump.log &

It's a warning, not an error. You expected it to be written to stderr, but you've established it's written to stdout. — Elliott Frisch
– Elliott Frisch, Commented Nov 22, 2022 at 12:11
@ElliottFrisch I dont really understand. Please enlighten. Do you mean "2" only referring to error but not warning? Is there any dedicated number represent warning? — Coisox
– Coisox, Commented Nov 22, 2022 at 13:52
nohup mysqldump -uuser -ppassword --comments --single-transaction --quick mydb desired_table | grep -v Warning | gzip >dump.sql.gz 2>/dev/null & will just ignore any warnings. — Elliott Frisch
– Elliott Frisch, Commented Nov 22, 2022 at 14:10
It literally just ignores any warnings. This is not generally recommended. — Elliott Frisch
– Elliott Frisch, Commented Nov 22, 2022 at 14:39

Bill Karwin · Accepted Answer · 2022-11-22 15:37:26Z

2

To redirect the stderr of the mysqldump command before sending it to gzip, do that before the pipe.

nohup mysqldump -uuser -ppassword --comments --single-transaction \
   --quick mydb desired_table 2>/dev/null | gzip >dump.sql.gz  &

This is not related to your stderr redirection question, but I would also recommend using an options file instead of putting user and password on the command line.

answered Nov 22, 2022 at 15:37

Bill Karwin

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2 Comments

Coisox Over a year ago

Thank you its working. I'm getting better of understanding after ur sample. But I wonder why with ur code, when I execute, the terminal back to prompt (as if the process has done but actually still running). Compare to my original code where the terminal display " nohup: ignoring input and redirecting stderr to stdout" and I have to CTRL+C to get the prompt

Bill Karwin Over a year ago

The & at the end of the command line puts the whole process into the background. Here's a good article covering the basics of job control in the bash shell: digitalocean.com/community/tutorials/…

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