How to use mod_exec proftpd linux

Question

i used this code to execute external script, from mod_exec proftpd.

ExecEngine on ExecLog /opt/proftpd_mod_exec.log ExecOptions logStderr logStdout

<IfUser yogi>
    ExecBeforeCommand STOR,RETR /home/yogi/Desktop/kab.sh EVENT=BeforeCommand FILE='%f'
    ExecOnCommand STOR,RETR /home/yogi/Desktop/kab.sh EVENT=OnCommand FILE='%f'
</IfUser>

but i get error code like this on proftpd_mod_exec.log file. STOR ExecBeforeCommand '/home/yogi/Desktop/kab.sh' failed: Exec format error

how can i fix it?

Answer 1

from http://www.proftpd.org/docs/contrib/mod_exec.html

This module will not work properly for logins, or for logins that are affected by DefaultRoot. These directives use the chroot(2) system call, which wreaks havoc when it comes to scripts. The path to script/shell interpreters often assume a certain location that is no longer valid within a chroot. In addition, most modern operating systems use dynamically loaded libraries (.so libraries) for many binaries, including script/shell interpreters. The location of these libraries, when they come to be loaded, are also assumed; those assumptions break within a chroot. Perl, in particular, is so wrought with filesystem location assumptions that it's almost impossible to get a Perl script to work within a chroot, short of installing Perl itself into the chroot environment.

From the error message it sounds like that just that. You have enabled chroot and the script cannot get executed because of files not available at expected places within chroot.

Author suggest not to use the module because of this. To get it work You need to figure out the dependencies You need in the chroot target and set them up there at the appropriate places. Or disable chroot for the users and try again. Third possibility: build a statically linked binary with almost no dependencies.

Or try, as the author of the module suggest, to use a FIFO and proftpd logging functionality to trigger the scripts outside of the chroot environment.