IBM has positioned AIX 5 L version 5.1, as the new standard in Unix operating systems. It is built upon AIX 4.3.3 and provides improvements in critical areas such as reliability, availability, performance and security. The recommended way to harden the AIX Operating System is to use the principle of least privilege. If the user does not need the service, they are not allowed to access that service. Also if the server is to be an application server, only allow those specific services like ports 80 443 and 8080 to the server. There is a security principle that says you should configure computers to provide only selected network services. The basic idea is this, every network service you offer is an opportunity for the bad guys (alternatively a risk to your system). That's not to say that you shouldn't offer any services -- a web application server that doesn't offer web services isn't very useful. Instead, the principle says you should have a good understanding of network services and you should not offer any service unless there are very good reasons for doing so. This paper offers reasons to harden both server and network services for AIX 5.1 -- an application of the security principle.
Some security packages address the problem by stripping all (or nearly all) network services and then instruct you to be careful about what you add to the system. That's a great approach but requires that you "get your hands on" the system before anyone layers anything onto it and you understand what you're adding to the system when you add it back in. These are two conditions that do not apply at many sites. The approach here is different. We will consider services offered by the AIX 5.1 operating system, try to explain what each does, note the risks involved with each and make recommendations about what one ought to do to mitigate the risk.
Planning - This is the part of the plan where you must define the overall security policies and goals. In many Organizations, this initial step is performed at the corporate level, and is likely to have already been completed.
Architecture - This is where the design of your environment is defined to meet the requirements of the planning phase.
Implementation - This is where the infrastructure is built from the architectural design.
Monitoring - Once the infrastructure is built, you will need to continuously monitor it for vulnerabilities and suspected attacks. A better approach might be to schedule weekly audits, so as not to choke the network with useless snmp traffic. Problems that are found here should then be addressed through the previous phases in order to find the best resolution possible.
Incident Response - This is the phase that you must address your worse fears. The worst time to begin working on this phase is after an attack or breach that has already occurred. The time spent in the beginning considering how you should respond to a real attack will pay for itself many times over if you are ever in this situation. You must think of this "Pre-emptive" thinking.
Your organization's security policy for networked systems should require that a detailed computer deployment plan be developed, implemented, and maintained whenever computers are being deployed. Access to your deployment plan should only be given to those who require the information to perform their jobs. All new and updated servers be installed, configured, and tested in a stand-alone mode or within test networks (i.e., not connected to operational networks). You must present a policy that defines in detail appropriate behavior within it's I/T infrastructure. All servers present a warning banner to all users indicating that they are legally accountable for their actions and, by using the servers, they are consenting to having their actions logged.
You must develop a server deployment plan that includes security issues. Most deployment plans address the cost of the computers, schedules to minimize work disruption, installation of applications software, and user training. In addition, you need to include a discussion of security issues. You can eliminate many networked systems vulnerabilities and prevent many security problems if you securely configure computers and networks before you deploy them. Vendors typically set computer defaults to maximize available functions, so you usually need to change defaults to meet your organization's security requirements. You are more likely to make decisions about configuring computers appropriately and consistently when you use a detailed, well-designed deployment plan. Developing such a plan will support you in making some of the hard trade-off decisions between functionality and security. Consistency is a key factor in security, because it fosters predictable behavior. This will make it easier for you to maintain secure configurations and help you to identify security problems (which often manifest themselves as deviations from common, expected behavior). Refer to the better practice that keeping the AIX operating system and applications software up to date, is an essential part of this strategy.
Identify the purpose of each computer. Document how the computer will be used. Consider the following:
Identify the network services that will be provided on the server. Servers as a general rule should be dedicated to a single service. This usually simplifies the configuration, which reduces the likelihood of configuration errors. In the case of the servers, the application server should be limited to www or https services. The db2 server should be ports 50000 (db2idb2inst1) and 50001 (db2idb2inst1). It also can eliminate unexpected and unsafe interactions among the services that present opportunities for intruders. In some cases, it may be appropriate to offer more than one service on a single host computer. For example, the server software from many vendors combines the file transfer protocol (FTP) and the hypertext transfer protocol (HTTP) services in a single package. It may be appropriate to provide access to public information via both protocols from the same server host but we do not recommend this as it is a less secure configuration.
Determine how the servers will be connected to your network. There are concerns relating to network connections that can affect the configuration and use of any one computer. Many organizations use a broadcast technology such as Ethernet for their local area networks. In these cases, information traversing a network segment can be seen by any computer on that segment. This suggests that you should only place "trusted" computers on the same network segment, or else encrypts information before transmitting it. These servers should be in there own private subnet.
Develop and follow a documented procedure for installing an operating system. I have compiled a separate document that pertains to this bullet. In this document, the steps to implement and install a base AIX 5.1 image are detailed and described with all the parameters that are set during installation. Make all your parameter choices explicit, even if they match the default settings. (This may seem to be unnecessary, but it can prevent security problems if you subsequently reuse your scripts or configuration files to configure servers). Your explicit choices will still be used even if the defaults have changed with new AIX releases. Your installation procedure should also specify the security-related updates or patches that are to be applied to the operating system. If possible, have a single person perform the installation procedure for each computer and capture each installation step in a documented manner (such as through using a checklist).
The most common approach is the use of passwords; but other mechanisms can be used, such as keys, tokens, and biometric devices (devices that recognize a person based on biological characteristics such as fingerprints or patterns of the retinal blood vessels). Because authentication mechanisms like passwords require information to be accessible to the authentication software, carefully document how that information will be protected. Authentication data is critical security information that requires a high level of protection. You should follow the security group's guidelines for administrative access into your sensitive data environment. In other words, password length of 8 characters with at least 2 alpha characters, etc. We will be discussing this in more detail in the recommendations section of this document.
Determine how appropriate access to information resources will be enforced. For many resources, such as program and data files, the access controls provided by AIX are the most obvious means to enforce access privileges. Also, consider using encryption technologies to protect the confidentiality of sensitive information. In some cases, protection mechanisms will need to be augmented by policies that guide user's behavior related to their workstations. Identify the users or categories of users of the computer. The categories are based on user roles that reflect their authorized activity. The roles are often based on similar work assignments and similar needs for access to particular information resources-system administrators, software developers, data entry personnel, etc. If appropriate, include groups of remote users and temporary or guest users. Document the categories of users that will be allowed access to the provided services. You may need to categorize users by their organizational department, physical location, or job responsibilities. You also need a category of administrative users who will need access to administer the servers and possibly another category for backup operators.
Access to AIX servers should be restricted to only those administrators responsible for operating and maintaining the server. This will ensure that the server's users are restricted to those who are authorized to access the provided service and responsible for server administration. Determine the privileges that each category of user will have on the servers. To document privileges, create a matrix that shows the users or user categories (defined in the previous step) cross-listed with the privileges they will possess. The privileges are customarily placed in groups that define what system resources or services a user can read, write, change, execute, create, delete, install, remove, turn on, or turn off. Decide how users will be authenticated and how authentication data will be protected. There are usually two kinds of authentication: (1) the kind provided with the operating system, commonly used for authenticating administrative users and (2) the kind provided by the network service software, commonly used for authenticating users of the service. A particular software implementation of a network service may use the provided authentication capability, and thus it may be necessary for users of that service to have a local identity (usually a local account) on the server.
Document procedures for backup and recovery of information resources stored on the computer. Possessing recent, secure backup copies of information resources makes it possible for you to quickly restore the integrity and availability of information resources. Successful restoration depends on configuring the operating system, installing appropriate tools, and following defined operating procedures. You need to document backup procedures including roles, responsibilities, and how the physical media that store the backup data are handled, stored, and managed. Consider using encryption technologies like ssh to protect backups. Your backup procedures need to account for the possibility that backup files may have been compromised by an undetected intrusion. Verify the integrity of all backup files prior to using them to recover systems.
Here are the tools that are used in I/T environments today. These tools are freeware, but have been validated by there reliability over the last 5 - 10 years.
|Tool||Purpose||Extent of usage||Comments|
|md5||Validate integrity of file contents||Daily (automated)||freeware|
|tripwire or AIDE||Verify integrity of directories and files on the server||Daily (automated)||freeware|
|tcp_wrapper||Log unauthorized connections to servers||Daily (Viewing of logs)||freeware|
|syslog||Collect log information for unauthorized entry on the server||Daily (Automated)||Part of Operating System|
|swatch||Log parsing tool, that makes log reader more bearable||Daily (Automated)||freeware|
|lsof||Monitors service/port connections to server||Daily (Automated)||freeware|
|ssh||To encrypt connections to servers||Daily (Automated)||freeware|
|tcpdump||Analyze packets on the servers interface||Daily (Automated)||freeware|
|ethereal||Packet capturing tool||Daily (Automated)||freeware|
|openssl||Encapsulation/tunneling of||Communication paths||freeware|
|nmap||Network exploration tool and security scanner||Weekly(Automated)||freeware|
|nessus||Network scanner and vulnerability assessment tool||Weekly (Automated)||freeware|
The best way to approach this portion of the checklist is to do a comprehensive physical inventory of the servers. Serial numbers and physical location would be sufficient.
Next we want to gather a rather comprehensive list of both the AIX and pseries inventories. By running these next 4 scripts we can gather the information for analyze.
Run these 4 scripts: sysinfo, tcpchk, nfsck and nethwchk. (See Appendix A for scripts)
By default the Unix operating system gives us 1024 services to connect to, we want to parse this down to a more manageable value. There are 2 files in particular that we want to parse. The first, is the /etc/services file itself. A good starting point is to eliminate all unneeded services and add services as you need them. Below is a screenshot of an existing ntp server etc/services file on one of my lab servers.
# # Network services, Internet style # ssh 22/udp ssh 22/tcp mail auth 113/tcp authentication sftp 115/tcp ntp 123/tcp # Network Time Protocol ntp 123/udp # Network Time Protocol # # UNIX specific services # login 513/tcp shell 514/tcp cmd # no passwords used
This file starts the daemons that we will be using for the tcp/ip stack on AIX servers. By default the file will start the sendmail, snmp and other daemons. We want to parse this to reflect what functionality we need this server for. Here is the example for my ntp server.
# Start up the daemons # echo "Starting tcpip daemons:" trap 'echo "Finished starting tcpip daemons."' 0 # Start up syslog daemon (for error and event logging) start /usr/sbin/syslogd "$src_running" # Start up Portmapper start /usr/sbin/portmap "$src_running" # Start up socket-based daemons start /usr/sbin/inetd "$src_running" # Start up Network Time Protocol (NTP) daemon start /usr/sbin/xntpd "$src_running"
This helps also to better understand what processes are running on the server.
Be aware of what is in the /etc/inittab file on the AIX servers. This file works like the registry in a Microsoft environment. If an intruder wants to hide a automated script, he would want it launched here or in the cron file. Monitor this file closely.
This is the AIX system file that starts system services, like telnet, ftp, etc. We also want to closely watch this file to see if there are any services that have been enabled without authorization. If you are using ssh for example this is what the inetd.conf file should look like. Because we are using other internet connections, this file is not used in my environment and should not be of use to you. This is why ssh should be used for all administrative connections into the environment. It provides an encrypted tunnel so connection traffic is secure. In the case of telnet, it is very trivial to sniff the UID and password.
## protocol. "tcp" and "udp" are interpreted as IPv4. ## ## service socket protocol wait/ user server server program ## name type nowait program arguments ##
This is network configuration file used by AIX. This is the file you use to set your default network route along your no (for network options) attributes. Because the servers will not be used as routers to forward traffic and we do not want to use loose source routing at You, we will be making a few changes in this file. A lot of them are to protect from DOS and DDOS attacks from the internet. Also protects from ACK and SYN attacks on the internal network.
################################################################## ################################################################## # Changes made on 06/07/02 to tighten up socket states on this # server. ################################################################## if [ -f /usr/sbin/no ] ; then /usr/sbin/no -o udp_pmtu_discover=0 # stops autodiscovery of MTU /usr/sbin/no -o tcp_pmtu_discover=0 # on the network interface /usr/sbin/no -o clean_partial_conns=1 # clears incomplete 3-way conn. /usr/sbin/no -o bcastping=0 # protects against smurf icmp attacks /usr/sbin/no -o directed_broadcast=0 # stops packets to broadcast add. /usr/sbin/no -o ipignoreredirects=1 # prevents loose /usr/sbin/no -o ipsendredirects=0 # source routing /usr/sbin/no -o ipsrcrouterecv=0 # attacks on /usr/sbin/no -o ipsrcrouteforward=0 # our network /usr/sbin/no -o ip6srcrouteforward=0 # from using indirect /usr/sbin/no -o icmpaddressmask=0 # dynamic routes /usr/sbin/no -o nonlocsrcroute=0 # to attack us from /usr/sbin/no -o ipforwarding=0 # Stops server from acting like a router fi
This computer system is the private property of XYZ Insurance. It is for authorized use only. All users (authorized or non-authorized) have no explicit or implicit expectations of privacy. Any or all users of this system and all the files on this system may be intercepted, monitored, recorded, copied, audited, inspected and disclosed to XYZ Insurance's management personnel. By using this system, the end user consents to such interception, monitoring, recording, copying, auditing, inspection and disclosure at the discretion of such personnel. Unauthorized or improper use of this system may result in civil and/or criminal penalities and administrative or disciplinary action, as deemed appropriate by said actions. By continuing to use this system, the individual indicates his/her awareness of and consent to these terms and conditions of use. LOG OFF IMMEDIATELY if you do not agree to the provisions stated in this warning banner.
root: loginretries = 5 - failed retries until account locks rlogin = false - Disables remote herald access to a root shell. Need to su from another UID. admgroups = system minage = 0 - minimum aging is no time value maxage = 4 - maximum aging is set to 30 days or 4 weeks umask = 22
This is an attribute that should be changed due to a runaway resource hog. This orphaned process can grow to use an exorbinate amount of disk space. To prevent this we can set the ulimit value here.
default: #fsize = 2097151 fsize = 8388604 - sets the soft file block size to a max of 8 Gig.
Set the $TMOUT variable in /etc/profile. This will cause a open shell to close after 15 minutes of inactivity. It works in conjunction with the screensaver, to prevent an open session to be used to either delete the server or worse corrupt data on the server.
# Automatic logout, include in export line if uncommented TMOUT=900
This is a nice piece of code, that the system administrators can use in order to allow "root-like" functionality. It allows an non-root user to run system binaries or commands. The /etc/sudoers file is used to configure exactly what the user can do. The service is configured and running on ufxcpidev. The developers are running a script called changeperms in order to tag there .ear files with there own ownership attributes.
First we setup sudo to allow root-like or superuser doer access to sxnair.
# sudoers file. # # This file MUST be edited with the 'visudo' command as root. # # See the sudoers man page for the details on how to write a sudoers file. # # Host alias specification # User alias specification # Cmnd alias specification # User privilege specification root ALL=(ALL) ALL sxnair,jblade,vnaidu ufxcpidev=/bin/chown * /usr/WebSphere/AppServer/installedApps/* # # # Override the built in default settings Defaults syslog=auth Defaults logfile=/var/log/sudo.log
These are some of the changes to the /etc/security/user file that will promote a more heightened configuration of default user attributes at your company.
default: umask = 077 - defines umask values - 22 is readable only for that UID pwdwarntime = 7 - days of password expiration warnings loginretries = 5 - failed login attempts before account is locked histexpire = 52 - defines how long a password cannot be re-used histsize = 20 - defines how many previous passwords the system remembers minage = 2 - minimum number of weeks a password is valid maxage = 8 - maximum number of weeks a password is valid maxexpired = 4 - maximum time in weeks a password can be changed after it expires minalpha = 2 - minimum number of alphabetic characters in a password minother = 1 - number of non-alphabetic characters in a password minlen = 8 - minimum character length of a password mindiff = 3 - number of different characters that must be used in a password maxrepeats = 2 - number of times a character can appear in a password
Set login attributes to be more restrictive in /etc/security/login.cfg
default: sak_enabled = false logintimes = logindisable = 5 logininterval = 0 loginreenable = 30 logindelay = 10 herald = "Unauthorized use prohibited.\r\nlogin: " usw: shells = /bin/sh,/bin/bsh,/bin/csh,/bin/ksh,/bin/tsh,/usr/bin/sh,/usr/bin/bsh,/usr/bin/csh,/usr/bin/ksh,/usr/bin/tsh maxlogins = 16 logintimeout = 15 - sets the time to 15 seconds from when a login is presented and you type in your password.
errpt -a|more alog -o -f '/var/adm/ras/bootlog' (boot log) who /var/adm/sulog who /var/adm/wtmp
The central loghost is lab_test.
# # M. Desrosiers of ITSecure, Inc. added these lines on 06/12/02 # # log all warnings # *.warning /var/log/syslog/warning rotate time 1d # rotate daily *.warning @loghost # # log mail debug messages # mail.debug /var/log/syslog/mail rotate time 1d # rotate daily mail.none /var/log/syslog/mail # log security messages # auth.debug /var/log/syslog/security rotate time 1d # rotate daily auth.notice @loghost # # system problems and events # *.alert;*.crit * *.emerge;*.alert;*.crit;*.err @loghost # # all other messages not including mail #
Today's computing environments are mostly distributed infrastructures. Your company must develop intrusion detection strategies for the servers. I do not believe that there are any sensors on the nternal network. Many of the common intrusion detection methods depend on the existence of various logs that AIX can produce and on the availability of auditing tools that analyze those logs. This will help you with installing the appropriate software tools and configure these tools and the operating system to collect and manage the necessary information. Keep your computer deployment plan current. Your company must update the computer deployment plan when relevant changes occur. Sources of change may include new technologies, new security threats, updates to your network architecture, the addition of new classes of users or new organizational units, etc. The environment will only work if the process is centralized. I also believe that there is not enough on-site experience and internal infrastructure to administor this project. The issues of 24/7 availability and the underlying issues of security in layers have to be addressed.
#!/bin/ksh # # This script is one of the system management tools used # to determine a particular AIX system configuration # # list all of the users registered on the system # /usr/sbin/lsuser -c -a id home ALL | sed '/^#.*/d' | tr ':' '\011' # # display the mounted filesystems # echo "*********************" echo echo LIST OF MOUNTED FILESYSTEMS echo echo "*********************" /usr/bin/df echo "*********************" echo echo echo "*********************" echo echo VOLUME GROUP INFORMATION echo echo "*********************" # # list out the volume group information # such as phy vol, logical vol info # /usr/sbin/lsvg '-p' rootvg /usr/sbin/lsvg '-l' rootvg /usr/sbin/lspv hdisk0 /usr/sbin/lspv '-p' hdisk0 /usr/sbin/lspv '-l' hdisk0 /usr/sbin/lspv hdisk1 /usr/sbin/lspv '-p' hdisk1 /usr/sbin/lspv '-l' hdisk1 # # list out all of the defined user groups # echo "****************" echo echo echo "****************" echo echo DEFINED USER GROUPS echo echo "****************" echo /usr/sbin/lsgroup '-c' ALL # # list out the TCP net info # echo "****************" echo echo echo "****************" echo echo TCP/IP NETWORK INFORMATION echo echo "****************" /usr/bin/netstat '-nr' /usr/bin/namerslv '-s' '-I' /usr/bin/hostent '-S' /usr/bin/inetserv '-s' '-S' '-X' # # display what software is installed on the system # echo "****************" echo echo echo "****************" echo echo SOFTWARE INVENTORY echo echo "****************" echo /usr/bin/uname '-x' /usr/bin/lslpp '-l' /usr/sbin/lsdev '-C' | sort '-d' '-f' /usr/bin/lssrc '-g' 'nfs' /usr/bin/pwdck '-n' 'ALL' /usr/bin/usrck '-n' 'ALL' /usr/sbin/grpck '-n' 'ALL' # # display the failedlogin log # echo "****************" echo echo FAILED LOGINS ON THIS SYSTEM echo echo "****************" /usr/bin/who '-s' '/etc/security/failedlogin' # # display the userid in each defined group # echo "****************" echo echo USER INFORMATION echo echo "****************" /usr/sbin/lsgroup '-fa' 'id' 'users' 'ALL' # and some other user info /usr/sbin/lsuser '-fa' 'id' 'groups' 'home' 'auditclasses' 'login' \ 'su' 'rlogin' 'telnet' 'ttys' 'ALL' tcpchk: # # this file check for tcp related files to see if it is # installed on the machine # echo "The following network products are installed on this system:" echo " " lslpp -l |grep bosnet echo " " installtest=`lslpp -l | /bin/grep 'bos.net.tcp'` if [ "x$installtest" = "x" ]; then echo "TCP/IP not installed" else echo "The following TCP/Ip services are configured on this machine" echo " " lssrc -g tcpip echo " " echo "******** WARNING **********" echo ".rhosts and .netrc are a security risk" echo ".rhosts files and .netrc files are in: " echo " " find / -name '.rhosts' -print echo " " echo ".netrc files are in:" echo " " find / -name '.netrc' -print echo " " if [ -x /usr/sbin/inetd -a -f /etc/hosts.equiv ]; then echo " the following hosts are allowed to rsh, rcp, rlogin" echo cat /etc/hosts.equiv | grep -v "#" echo " " fi if [ -x /usr/sbin/inetd -a -f /etc/hosts.lpd ]; then echo " the following hosts are allowed to sbumit remote print jobs" echo " ONLY" cat /etc/hosts.lpd | grep -v "#" echo " " fi if [ -x /usr/sbin/inetd -a -f /etc/resolv.conf ]; then echo "this machine is on a nameserver network" echo " " cat /etc/resolv.conf | grep -v "#" fi fi exit 0
#!/bin/sh # # this script review the NFS configuration for a machine # echo "NFS Configuration" echo "-----------------" echo " " installtest=`lslpp -l |/bin/grep nfs` if [ "x$installtest" = "x" ]; then echo "NFS not installed on this system" echo " " else echo "NFS is installed on this system" echo " " nfstest=`lssrc -g nfs|/bin/grep active` if [ "x$nfstest" = "x" ]; then echo "NFS is not active at this time" echo " " else echo "NFS is active" echo " " if [ -x /usr/etc/nfsd -a -f /etc/exports ]; then echo "This machine is an NFS server" :q! kashmir@root /usr/local/bin > cat nfschk #!/bin/sh # # this script review the NFS configuration for a machine # echo "NFS Configuration" echo "-----------------" echo " " installtest=`lslpp -l |/bin/grep nfs` if [ "x$installtest" = "x" ]; then echo "NFS not installed on this system" echo " " else echo "NFS is installed on this system" echo " " nfstest=`lssrc -g nfs|/bin/grep active` if [ "x$nfstest" = "x" ]; then echo "NFS is not active at this time" echo " " else echo "NFS is active" echo " " if [ -x /usr/etc/nfsd -a -f /etc/exports ]; then echo "This machine is an NFS server" echo "The following directories may be exported:" echo " " cat /etc/exports echo " " echo "The following directories are currently exported:" echo " " cat /etc/xtab echo " " echo "The following hosts have exported directories mounted" echo "at this time" echo " " /usr/bin/showmount echo " " else echo "this machine is an NFS client" echo " " echo "The following directories are mounted from remote systems" echo " " echo "Node mounted mounted over vfs date options" mount | grep -v "^ " echo " " fi echo "The following NFS services are configured on this machine:" echo " " lssrc -g nfs echo " " fi echo " " echo "NIS Configuration" echo "-----------------" isypset=`domainname | /bin/grep "^[a-zA-Z]"` if [ "x$isypset" = "x" ]; then echo "NIS is not configured at this time" echo " " else echo "NIS is configured on this system" echo " " fi fi exit 0
The following network interfaces are available on this system: en0 Available 10-68 Standard Ethernet Network Interface en1 Defined 10-70 Standard Ethernet Network Interface en2 Defined 10-80 Standard Ethernet Network Interface et0 Defined 10-68 IEEE 802.3 Ethernet Network Interface et1 Defined 10-70 IEEE 802.3 Ethernet Network Interface et2 Defined 10-80 IEEE 802.3 Ethernet Network Interface lo0 Available Loopback Network Interface The following communication interfaces are brought up at boot Loopback interfaces are not used for communication en0 The current interface is: en0: flags=4e080863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,PSEG> inet 192.168.1.13 netmask 0xffffffe0 broadcast 192.168.1.31 kashmir@root /usr/local/bin > more nethwchk #!/bin/sh # # check the network interface hardware # echo "The following network interfaces are available on this system:" echo " " lsdev -C -c if echo " " echo "The following communication interfaces are brought up at boot" echo " " echo "Loopback interfaces are not used for communication " echo " " odmget -q"value='up'" CuAt | grep name|cut -c10-12 echo " " iftest=`odmget -q"value='up'" CuAt|grep name|cut -c10-12` echo "The current interface is: " echo " " for i in $iftest do if [ -n $i ]; then ifconfig $i echo " " fi done exit 0