echo and cat : write error: Invalid argument

rey · 05-17-2012, 04:52 PM

hello
i'm trying to write to this file

Code:

/proc/net/xt_recent/recent_blocked

however my commands have failed even executed as root:

Code:

cat $DIR/recents > /proc/net/xt_recent/recent_blocked
cat: write error: Invalid argument

that file stores some blocked ip addresses for iptables,
i need to know how to write to this file to make my
scripts work, i have searched a lot without clear results

thanks for your help

Didier Spaier · 05-17-2012, 05:20 PM

cat is for reading the values in the /proc file system.

To write, you shoud use echo:

Code:

echo $DIR/recents > /proc/net/xt_recent/recent_blocked

Of course, you can write only one value at a time.

And keep in mind that /proc store only one value in each "file", thus $DIR/recents should contain only one value.

rey · 05-17-2012, 05:26 PM

sorry, if you echo a filename you get the same file name, not the contents
cat is for reading the file contents!!!

in your example you get the very same file path

any other ideas?

Didier Spaier · 05-17-2012, 05:36 PM

Quote:

Originally Posted by rey

sorry, if you echo a filename you get the same file name, not the contents
cat is for reading the file contents!!!

That's right, but on the other hand you can't redirect the output of cat to /proc.

EDIT Out of curiosity, why use /proc to store the blocked ip addresses?

Tinkster · 05-17-2012, 05:47 PM

Quote:

Originally Posted by rey

hello
i'm trying to write to this file

Code:

/proc/net/xt_recent/recent_blocked

however my commands have failed even executed as root:

Code:

cat $DIR/recents > /proc/net/xt_recent/recent_blocked
cat: write error: Invalid argument

that file stores some blocked ip addresses for iptables,
i need to know how to write to this file to make my
scripts work, i have searched a lot without clear results

thanks for your help

Use iptables to write iptables rules/stats.

proc, for the most part, is read-only; it's a view into
the running kernel, not a saloon door.

Cheers,
Tink

rey · 05-17-2012, 05:57 PM

Quote:

Originally Posted by Didier Spaier

EDIT Out of curiosity, why use /proc to store the blocked ip addresses?

that's how iptables work, it has a 'recent' module and the manual says that you can add
ip addresses to block them automatically, without adding extra rules

Quote:

/proc/net/ipt_recent/* are the current lists of addresses and information about each entry of each list.
Each file in /proc/net/ipt_recent/ can be read from to see the current list or written two using the following commands to modify the list:

echo xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
to Add to the DEFAULT list
echo -xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
to Remove from the DEFAULT list

neither works for me, i'm running ubuntu 10.04 lucid
i wonder why it seems to work for other setups

thanks for your comments