Registered User's questions

Here is a situation when I do
root@skd:~# service networking restart
restart: Unknown instance:
and when I do
root@skd:~# service networking stop
stop: Unknown instance:

now if I do

/etc/init.d/networking stop  
  * Deconfiguring network interfaces...       Ignoring unknown interface eth1=eth1.
[ OK ]

note above I did not used service command and it shows working.

and now if I start it in same way I get a warning.

/etc/init.d/networking start
Rather than invoking init scripts through /etc/init.d, use the service(8)
utility, e.g. service networking start

Since the script you are attempting to invoke has been converted to an
Upstart job, you may also use the start(8) utility, e.g. start networking
networking stop/waiting

In any case either service command or using /etc/init.d/networking with restart does not do any thing. It does not work and neither does it start.Is it ia problem with Ubuntu 10.04 that service utility does not work properly?

I was using nmap to scan the mac addresses of my network.What I found was internet connections and rest of network services badly clogged the users were not able to connect to internet.After messing with different things some times later we noticed on one of machines I was running nmap and stopping it did the trick.

nmap -sP 192.168.1.0/20

Is what I was trying and it basically clogged the entire network. Can some one suggest what can be a remedy for same and why it actually happened?

EDIT

As some people suggested below it generates a lot of ARP traffic
1) is there a way I can measure this ARP traffic?
2) In this case since user applications could not reach internet is there some way I can detect congestion in network.Here nmap was run by me as root so I knew but for future I want to know.

lsof | grep /var is giving me following error

lsof: WARNING: can't stat() fuse.gvfs-fuse-daemon file system /home/user/.gvfs
  Output information may be incomplete.

what can be possible reason for it?

We are testing one of our production server with ab and what we found is

apr_socket_recv: Connection timed out (110)
Total of 176 requests completed

after some time above output.That means the server could not handled 200 requests? Or what exactly could be the problem and how to reach to the bottom of it?

I am running this command to find out the files which were modified in last 10 minutes

 find / -fstype local -mtime -10m

but it is giving following error each time

find: missing argument to `-mtime'

What is wrong with above?

here is a practical situation.I facing some of my files where there is a common string in these files.I usually will open vi and do some thing like

:%s/text/replacement/g

and I have to do it in many files many many times. Is there some easy way to do it or some sort of alias that I can create for the same?

Is there some easy way to find out mac address of all machines on my network rather than doing an SSH into each and ifconfig | grep HWaddr if there are 300 machines on network I really need some easy solution.

 file * |  grep 'ASCII text' | chmod -x 
chmod: missing operand
Try `chmod --help' for more information.

The above command gives me error.Basically I am trying to find all the files whose type is ASCII and change their permissions to -x.What mistake is there in above syntax?

I am having a situation where I can not use a CD or PxE boot or wubi to install.I need to necessarily do an http install of Ubuntu.I am basically trying to create a guest OS in a virtualization setup on Xen on a non VT hardware.On a non VT hardware the virt-manager does not allow to install from local ISO or PXE even the only option is via a URL on http://

Here is what I did
1) Download ubuntu 10.04 32 bit ISO
2) Kept it in /var/www (apache2 is running)
3) renamed it to ubuntu.iso

and when I reached a stage where installation begins I gave path http://localhost/ubuntu.iso but I got an error any installable distribution not found.

4) After this I did

mkdir /var/www/sk

mount -t iso9660 /var/www/ubuntu.iso /var/www/sk -o loop

and this time during the installation I gave path http://localhost/sk I was able to see the contents in browser http://localhost/sk which you will see in a normal CD. But beginning installation I got same error

ValueError: Could not find an installable distribution at 'http://localhost/sk

So I want to just confirm if http install is done only this way or some other way because the installation is not proceeding.

I am having a server in a corporate data centre who's sys admin is me. There are some virtual machines running on it.The main server is accessible from internet via SSH. There are some people who within the lan access the virtual machines whose IPs on LAN are

192.168.1.1  
192.168.1.2  
192.168.1.3
192.168.1.4

the main machine which is a bastion host for internet has IP 192.168.1.50 and only I have access to it. I have to give people on internet the access to the internal machines whose IP I mentioned above.I know tunnel is a good way but the people are fairly non technical and do not want to get into a tunnel etc jargons.So I came across a solution as explained on this link On the gateway machine which is 192.168.1.50 in the .ssh/config file I add following

Host securehost.example.com     
ProxyCommand ssh [email protected] nc %h %p

Now my question is do I need to create separate accounts on the bastion host (gateway) to those users who can SSH to the inside machines and in each of the users .ssh/config I need to make the above entry or where exactly I put the .ssh/config on the gateway.

Also ssh [email protected]

where user1 exists only on inside machine 192.168.1.1 and not on the gateway is that right syntax? Because the internal machines are accessilbe to outside world as

site1.example.com
site2.example.com
site3.example.com
site4.example.com

But SSH is only for example.com and only one user.So How should I go for .ssh/config
1) What is the correct syntax for ProxyCommand on gateway's .ssh/config should I use
ProxyCommand ssh [email protected] nc %h %p or I should use

ProxyCommand    ssh [email protected] in nc %h %p

2) Should I create new user accounts on gateway or adding them in AllowedUsers on ssh_config is sufficient?

Following is my ifconfig output

eth0      Link encap:Ethernet  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:28 Base address:0x2000 

eth1      Link encap:Ethernet  
          inet addr:192.168.1.2  Bcast:192.168.1.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:36497 errors:0 dropped:0 overruns:0 frame:14515
          TX packets:44884 errors:1352 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:20781745 (20.7 MB)  TX bytes:17776225 (17.7 MB)
          Interrupt:17 Base address:0xc000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:12 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:720 (720.0 B)  TX bytes:720 (720.0 B)

virbr0    Link encap:Ethernet  
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:4416 (4.4 KB)

vmnet1    Link encap:Ethernet 
          inet addr:192.168.185.1  Bcast:192.168.185.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

vmnet8    Link encap:Ethernet  
          inet addr:192.168.207.1  Bcast:192.168.207.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

How do I use grep to extract the IP address corresponding to each LAN card?

Is that possible? How can it be achieved?

I am a bit confused with the abundant tcpdump tutorials on internet. I am having a few of the virtual machines running on a virtualization server.Where I am debugging a problem.Port 53 is the one in problem. I have a bridged setup where out of 4 LAN cards on the machine in question one is active and it is xen-br0 I want to check if there is any request coming on port 53 on the server by other machines on LAN in question. I also want to see if the guest operating systems on LAN or any other machine is sending traffic at port 53.Due to abundant messages being generated via tcpdump I am finding it difficult to grep the output at desired port.

So how can I use it if some one can give an example that would be helpful. Thanks in advance.

screen -list shows

There are screens on:
    9531.pts-0.ubuntu   (03/02/2011 12:43:34 PM)    (Detached)
    2101.pts-0.ubuntu   (03/02/2011 12:39:17 PM)    (Attached)
    2219.pts-0.ubuntu   (03/02/2011 11:20:56 AM)    (Attached)
3 Sockets in /var/run/screen/S-bond.

but when I type

screen -r 2101.pts-0.ubuntu
There is a screen on:
    2101.pts-0.ubuntu   (03/02/2011 12:39:16 PM)    (Attached)
There is no screen to be resumed matching 2101.pts-0.ubuntu.

Here I can not get back the the screen 2101.pts-0.ubuntu and infact I get exited. Where as if I do

screen -r 9531.pts-0.ubuntu
[detached from 9531.pts-0.ubuntu]

then above you can see I went inside that session and came out and I can do it again and again.But with other sessions same is not the case? SO what mistake am I doing?

I have used diff command in past.I faced a situation to which I did not had a clue here are some text strings (which can be stored in a file)

CONFIG_XEN=y
CONFIG_XEN_PVHVM=y
CONFIG_XEN_MAX_DOMAIN_MEMORY=128
CONFIG_XEN_SAVE_RESTORE=y
CONFIG_XEN_DEBUG_FS=y
CONFIG_SWIOTLB_XEN=y
CONFIG_MICROCODE_XEN=y
CONFIG_XEN_DOM0=y
CONFIG_XEN_PRIVILEGED_GUEST=y
CONFIG_XEN_DOM0_PCI=y
CONFIG_XEN_PCI_PASSTHROUGH=y
CONFIG_PCI_XEN=y
CONFIG_XEN_PCIDEV_FRONTEND=y
CONFIG_XEN_BLKDEV_FRONTEND=y
CONFIG_NETXEN_NIC=m
CONFIG_XEN_NETDEV_FRONTEND=m
CONFIG_XEN_KBDDEV_FRONTEND=y
CONFIG_HVC_XEN=y
CONFIG_XEN_FBDEV_FRONTEND=y
CONFIG_XEN_BALLOON=y
CONFIG_XEN_SCRUB_PAGES=y
CONFIG_XEN_DEV_EVTCHN=y
CONFIG_XEN_BACKEND=y
CONFIG_XEN_NETDEV_BACKEND=m
CONFIG_XEN_BLKDEV_BACKEND=m
CONFIG_XEN_BLKDEV_TAP=m
CONFIG_XEN_BLKBACK_PAGEMAP=m
CONFIG_XEN_PCIDEV_BACKEND=m
CONFIG_XEN_PCIDEV_BACKEND_VPCI=y
CONFIG_XENFS=y
CONFIG_XEN_COMPAT_XENFS=y
CONFIG_XEN_SYS_HYPERVISOR=y
CONFIG_XEN_MCE=y
CONFIG_XEN_XENBUS_FRONTEND=y
CONFIG_XEN_GNTDEV=y
CONFIG_XEN_S3=y
CONFIG_ACPI_PROCESSOR_XEN=y
CONFIG_XEN_PLATFORM_PCI=m

I have to basically find above strings only (not any other) in a .config file of kernel which looks as follows

http://pastebin.com/AEQ6p9Vm It is a very big file.

Now I had no clue if by commands I can find the entries I first mentioned whether exist in second file or not so I did manually copied each entry and searched in the .config I mentioned.I found

there are following differences

 # CONFIG_XEN_DEBUG_FS is not set CONFIG_XEN_BLKBACK_PAGEMAP <--- is
 completely missing
 # CONFIG_XEN_NETDEV_BACKEND is not set
 # CONFIG_XEN_BLKDEV_BACKEND is not set
 # CONFIG_XEN_BLKDEV_TAP is not set CONFIG_XENFS=y
 # CONFIG_XEN_GNTDEV is not set

Can this be easily done by find grep or some thing similar?

On one of my servers I have following in /etc/logrotate.d/apache2

/var/log/apache2/*.log {
        weekly
        missingok
        rotate 52
        compress
        delaycompress
        notifempty
        create 640 root adm
        sharedscripts
        postrotate
                if [ -f "`. /etc/apache2/envvars ; echo ${APACHE_PID_FILE:-/var/run/apache2.pid}`" ]; then
                        /etc/init.d/apache2 reload > /dev/null
                fi
        endscript
}
~                  

What I observed is I get each week a gz file. I do not want it to save just delete at the end of 15 days(or size 100M) how can this be done? What do I need to add above? It is a Ubuntu 10.04 server.

I am a Computer Science guy who understands networking very well. But when it comes to Web hosting companies I am clue less. I want to know how do web hosting companies give so many public IPs to so many users and each of them has root login also. How this is technically done that is what I am interested to know. I do not know how you people configure it.

In my case if I have to do I will buy a public IP from some one and connect my server to it and at max give some people SSH access to it.In case of Web hosting companies how is it done.

My some software applications need to relay emails to my email account.

The only way they can do it via connecting to localhost which relays mail on behalf of application.

I have forgotten the name of such a software it is a Debian/Ubuntu environment.

Can any one let me know the name of such an proxy software which relays mail to your local SMTP server on behalf of application I will need to enter username password also in this setting because the mail server needs authentication.

I use IPTABLES in /etc/network/interfaces

pre-up iptables-restore /etc/firewall.txt

I tried searching for some thing like /etc/init.d/iptables on Ubuntu but that does not seem to exist.So if I have to stop IPTABLE for temporarily for sysadmin work how can I do that?

I am trying to get a few Content Management Systems up and running. But I have security concerns with respect to them

1) please see following link http://www.dokeos.com/doc/installation_guide.html section 2 says The following directories need to be readable, writeable and executable for everyone:

• dokeos/main/inc/conf/
• dokeos/main/upload/users/
• dokeos/main/default_course_document/
• dokeos/archive/
• dokeos/courses/
• dokeos/home/

I am not very happy with this idea of having directories to be readable,writeable and executable for every one.

2) http://doc.claroline.net/en/index.php/Install_general_information

the section Rights on folders says

" If you don't want to set write access on the whole folders, which is recommended for security reasons, give to the web server user write access on these folders : "

Is this a recommended practice.?

3) Also another LMS (Learning Management System) while installing asked to give some folders writeable and executable for every one here is a link http://atutor.ca/atutor/docs/installation.php While installing it I got a message

“The directory you specify must be created if it does not already exist  

and be writeable by the webserver. On Unix machines issue the command chmod a+rwx content, additionally the path may not contain any symbolic links. chmod a+rwx /var/www/atutor/content”

4) Another LMS docebolms asked to give write permissions on

files/doceboCore/photo
files/common/users
files/doceboLms/course
files/doceboLms/forum
files/doceboLms/item
files/doceboLms/message
files/doceboLms/project
files/doceboLms/scorm
files/doceboLms/test

I checked its documentation http://www.docebo.org/doceboCms/index.php?mn=docs&op=docsπ=5_4&folder=7 but was not that helpful.

I am not at all convinced by the idea of giving permissions to read,write and execute as these Learning Management Systems say. Let me know what you people have to say? What is the best practise in such situations?

Hi on one of my server I have installed a lot of softwares where in for each application I have created a user name and password.After that these applications have been running.Now I have to remove these applications and install the latest version of softwares.I have to basically make every thing work from scratch.My problem is I have forgotten the user name and passwords for some of these databases.There are other user applications also if I completely remove mysql and then install every thing that will work for me but other applications will stop working. Is there a way I can recover or even reset these password I have a root account to database so if recovery is not possible I at least want to reset and delete these databases.All the accounts are on mysql.