I just wanted to increase the loglevel of the SFTP subsystem on one of my servers. That was not as easy as I thought:
The configuration file of the OpenSSH server /etc/ssh/sshd_config contains an entry for the SFTP subsystem:
Subsystem sftp /usr/libexec/openssh/sftp-server
Seems sftp-server allows the loglevel to be set:
# /usr/libexec/openssh/sftp-server -h
usage: sftp-server [-he] [-l log_level] [-f log_facility]
The manpage contains all the available loglevels. I tried adding the parameter “-i VERBOSE” in my sshd_config, but this fails, as my version of OpenSSH does not allow command-line arguments here. I’m using Centos 5.6 which comes with OpenSSH 4.3. Command-line parameter are available since OpenSSH 4.4 (http://www.openssh.com/txt/release-4.4)
So I created a file /usr/libexec/openssh/sftp-server-custom containing:
“/usr/libexec/openssh/sftp-server -i VERBOSE” and altered the line in sshd_config to:
Subsystem sftp /usr/libexec/openssh/sftp-server-custom
Restart or reload the ssh server so the configuration change gets active, and it starts logging nicely.