History of Computer Problem-Solution (Open) (No. 16)

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  • 1 (2009-04-26 (Sun) 01:23:07)
  • 2 (2009-04-26 (Sun) 01:23:59)
  • 3 (2009-05-08 (Fri) 08:39:27)
  • 4 (2009-05-18 (Mon) 21:55:43)
  • 5 (2009-06-01 (Mon) 21:39:07)
  • 6 (2009-06-02 (Tue) 10:21:13)
  • 7 (2009-06-04 (Thu) 00:16:54)
  • 8 (2009-07-02 (Thu) 12:35:59)
  • 9 (2009-07-02 (Thu) 21:46:59)
  • 10 (2009-07-17 (Fri) 16:01:58)
  • 11 (2009-09-09 (Wed) 13:12:19)
  • 12 (2009-10-10 (Sat) 13:06:29)
  • 13 (2010-01-06 (Wed) 22:37:13)
  • 14 (2010-01-13 (Wed) 23:18:23)
  • 15 (2010-01-17 (Sun) 15:41:21)
  • 16 (2010-01-19 (Tue) 16:12:51)
  • 17 (2010-04-29 (Thu) 15:24:51)
  • 18 (2012-03-29 (Thu) 10:42:18)
  • 19 (2012-08-29 (Wed) 17:46:04)
  • 20 (2012-09-25 (Tue) 17:01:48)
  • 21 (2012-09-26 (Wed) 12:18:33)
  • 22 (2012-10-02 (Tue) 17:01:00)
  • 23 (2013-06-03 (Mon) 17:13:46)
  • 24 (2013-06-05 (Wed) 14:43:13)
  • 25 (2013-08-26 (Mon) 10:20:51)
  • 26 (2013-10-24 (Thu) 09:04:54)
  • 27 (2014-01-17 (Fri) 18:53:28)
  • 28 (2014-07-24 (Thu) 11:35:12)
  • 29 (2014-08-04 (Mon) 10:01:23)
  • 30 (2014-08-05 (Tue) 10:03:57)
  • 31 (2014-08-05 (Tue) 13:01:22)
  • 32 (2014-08-13 (Wed) 10:14:22)
  • 33 (2014-08-14 (Thu) 05:43:40)
  • 34 (2014-08-18 (Mon) 11:43:55)
  • 35 (2014-08-19 (Tue) 12:27:17)
  • 36 (2014-08-22 (Fri) 15:15:39)
  • 37 (2014-08-22 (Fri) 15:53:33)
  • 38 (2014-10-14 (Tue) 17:07:51)
  • 39 (2014-10-17 (Fri) 14:16:07)
  • 40 (2015-08-06 (Thu) 15:02:09)
  • 41 (2016-03-10 (Thu) 11:11:59)

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This is a page of "How to" solve some computer problems that may happen.

P = problem; S = solution

P: (2010.01.19) Managing ntp†

S: ntp and ntpdate package have to be configured in some tricky ways†

• ntp.conf file

  [root@tube40 ~]# emacs /etc/ntp.conf

  The /etc/ntp.conf file is the main configuration file for Linux NTP in which we place the IP addresses of the servers we want to use. Here we only use one server:

  server  ntp.tohoku.ac.jp    # A stratum 1 server at tohoku.ac.jp
  #server  ntp.redhat.com     # A stratum 2 server at redhat.com

  We have to restart the NTP process every time we make a change to the configuration file for the changes to take effect on the running process.

• To get NTP configured to start at boot, use the line:

  [root@tube40 ~]# chkconfig ntpd on

• To start, stop and restart NTP after booting, follow these examples:

  [root@tube40 ~]# /etc/init.d/ntpd start
  [root@tube40 ~]# /etc/init.d/ntpd stop
  [root@tube40 ~]# /etc/init.d/ntpd restart

• For the synchronization, ntpd should be stopped and ntpdate should be run at least three times, then ntpd can be run again:

  [root@tube40 ~]# /etc/init.d/ntpd stop
  Shutting down ntpd:                                        [  OK  ]
  [root@tube40 ~]# /usr/sbin/ntpdate -u ntp.tohoku.ac.jp
  19 Jan 16:11:08 ntpdate[23079]: adjust time server 130.34.11.117 offset 0.016601 sec
  [root@tube40 ~]# /usr/sbin/ntpdate -u ntp.tohoku.ac.jp
  19 Jan 16:11:09 ntpdate[23080]: adjust time server 130.34.11.117 offset 0.015737 sec
  [root@tube40 ~]# /usr/sbin/ntpdate -u ntp.tohoku.ac.jp
  19 Jan 16:11:13 ntpdate[23081]: adjust time server 130.34.11.117 offset 0.014081 sec
  [root@tube40 ~]# /etc/init.d/ntpd start
  Starting ntpd:                                             [  OK  ]

P: (2010.01.13) The problem of 2010.1.6 is solved but response is slow.†

S: The problem is due to the fact that /etc/mtab is on root (not snapshot)†

Since we do not know what is the process of mount the file. we can not change mtab to snapshot. For a moment, we force mount /home1 and /rsaito on /tmp/home1, /tmp/rsaito

/etc/rc5.d/S28autofs stop
mkdir /tmp/home1
mkdir /tmp/rsaito
mount -n 192.168.2.100:/home1 /tmp/home1
mount -n 192.168.2.100:/rsaito /tmp/rsaito
df

/rsaito/bin/pxe-mount

P: (2010.1.6) /rsaito is not automountd on PXE client.†

S: edit and add flexS:/rsaito information on†

tube30:/nfsboot/root/etc/mtab

P: (2009.10.10) Gnorm logout is slow for Xming etc.†

This is a firewall problem of windows.

S: Open port 16001 tcp†

control panel -> firewall -> add new port ->

Name Esound
Port 16001
     TCP

P: (2009.07.17) Load average of FLEX is very high.†

This is due to mounting problem again (mount NFS). After checking mount status, it is found that a network harddisk was not unmounted nicely before turning off.

S: Re-mount (turn on) the harddisk, and do some safety procedure.†

• check mount status:

  # mount

• umount once (assuming mount point is /mnt/backup):

  # umount -f /mnt/backup

• synchronize several times:

  # sync
  # sync
  # sync

• check df or mount status again
• if the harddisk has been nicely unmounted, then it is safe to turn it off.

P: (2009.07.02) Flex is unstable for logining or e-mails.†

S: mount to tube:/home1-old was not allowed any more.†

comment out one line in /etc/auto.misc 
# home1    172.17.4.134:/home1-old

./S28autofs forcerestart

I also delete in /etc/exports 

the requests from 172.17.4.184 (nuguraha) 172.17.4.188 (mahabubu)
and 172.17.4.127 (furu).

exportfs -a

we also need to restart nfs
/etc/rc5.d/S60nfs restart

P: (2009.06.03) Today we were failed to run ether-wake command on new-PXE server/client machines using new Hub/router.†

S: We manually turn those on and off. After that ether-wake (wake-on-Lan) command was successful.†

P: PXE (network boot) is now installing 2009.5.1†

S: finished. status PXE Server (Open)†

P: We move /etc/passwd then we can not be root. No more even shutdown.†

S: cntl-alt-del and reboot. Then when OS selection, push any arrow.†

Then many selection of OS appears. Select one of OS, and press E. Then select kernel and press E again. Then you can edit the command for starting kernel and add "single" in the last of the command. Finally select "b" for booting and single user mode appears. Make /etc/passwd files and exit and runlevel 5 is recovers.

Even if we used NIS, we should not delete /etc/passwd /etc/group and /etc/shadow.

P: linux emacs ispell error (no language "eu") 2009.4.24†

S: solved. "M-x ispell-change-dictionary" and select english†

S: solved. Edit .emacs to add (setq ispell-dictionary "english")†

P: How to update the files of remote to the files of local†

S: solved. "rsync -avc -e ssh saito@remote:/home/saito/book09/ /rsaito/book09"†