Question : Monitor user connections to linux server

I have a linux (redhat 5) server that we use for sftp access for our installers and customers. Recently I was asked if I could report on user access and bandwidth usage (per user) as well as what resources they are accessing on the server. We need to be sure we don't have anyone else using this server for purposes outside what is was built for.

Any help is appreciated.

Answer : Monitor user connections to linux server

Here some scripts and compiled app:

TrafShow
http://soft.risp.ru/trafshow/index.shtml

MRTA - Multi Router Traffic Accounting
http://mrta.sourceforge.net/

MRTG - Multi Router Traffic Grapher
http://oss.oetiker.ch/mrtg/

NDSAD - captures IP-traffic from network interfaces and export NetFlow v.5
http://sourceforge.net/projects/ndsad/

TC - Traffic Counter
ftp://ftp.opennet.ru/pub/net/trafd/tc/

IPStat - IP accounting package for Linux with a Java Servlet/JSP Web interface
http://isp.od.ua/~rsi/

pmacct - Promiscuous mode IP Accounting package (Netflow v9 and IPv6)
http://www.ba.cnr.it/~paolo/pmacct/

IPACCO - collect, visualize and analyze IP accounting data
http://mpolk.members.easyspace.com/ipacco/index.html

Argus - network Audit Record Generation and Utilization System
http://qosient.com/argus/

Softflowd - network traffic analyser capable of Cisco NetFlow
http://www.mindrot.org/softflowd.html

LUTA - Local User Traffic Accounting
http://www.evpatoria.org/~vitalik/projects/luta.tar.gz

Net-Acct-MySQL
http://netacct-mysql.sourceforge.net/

traflog - program logging ip/tcp/udp sessions in MySQL/PgSQL
http://sourceforge.net/projects/traflog/

IPA - Pluggable Accounting System
http://ipa-system.sourceforge.net/

IPmeter - network usage metering and billing application for IP traffic
http://www.ipmeter.com/

iplog - TCP/IP traffic logger, capable of logging TCP, UDP, and ICMP traffic.
http://ojnk.sourceforge.net/

Bandwidth monitor - utility that allows the user to view the bandwidth currently being consumed to and fromeach network interface
http://packages.debian.org/unstable/net/bwm.html

Bandmin - record and log ip accouting data
http://online.securityfocus.com/tools/942

IP Flow Meter - bandwidth analysis tool, that measures how much bandwidth specified hosts use on their Internet link      
http://www.via.ecp.fr/~tibob/ipfm/


TAS - Traffic Accounting System, gather and process the traffic statistics from PC or Cisco routers
http://www.chelcom.ru/~anton/projects/tas/

Trafstat
http://redmine.shelek.su/projects/trafstat/wiki

Some billing systems:
Pyzzle.ISP - http://www.pyzzle.ru/
NetUP UTM - http://www.utm-billing.com/
LANBilling - http://www.lanbilling.ru/
IPStat - http://ipstat.perm.ru/