This is a page of "How to" solve some computer problems that may happen. P = problem; S = solution #contents ** P: (2012.08.29) Changing default text editor [#vf206db3] *** S: run this command: [#p639256c] sudo update-alternatives --config editor ** P: (2012.03.29) Segmentation fault when login tube [#j9c1a221] *** S: run this command /rsaito/bin/no-passwd [#d2e289e1] Then press Enter anytime the statement appears ** P: (2010.04.29) set-pathname-coding-system function does not exists in new xemacs lisp which existed in flex. [#t79f4d54] ** P: (2010.01.19) Managing ntp [#p100119] *** S: ntp and ntpdate package have to be configured in some tricky ways [#s100119] - 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. [#cc7513d1] *** S: The problem is due to the fact that /etc/mtab is on root (not snapshot) [#j127f4e3] 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. [#m92944ad] *** S: edit and add flexS:/rsaito information on [#q5d5939e] tube30:/nfsboot/root/etc/mtab ** P: (2009.10.10) Gnorm logout is slow for Xming etc. [#y54d795e] This is a firewall problem of windows. *** S: Open port 16001 tcp [#c4bf3cc3] control panel -> firewall -> add new port -> Name Esound Port 16001 TCP ** P: (2009.07.17) Load average of FLEX is very high. [#ba0d0fa4] 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. [#l1c8b137] - 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. [#ac90f02f] *** S: mount to tube:/home1-old was not allowed any more. [#e2a3634b] 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. [#m53007b8] *** S: We manually turn those on and off. After that ether-wake (wake-on-Lan) command was successful. [#a08cf22e] ** P: PXE (network boot) is now installing 2009.5.1 [#e8f71204] *** S: finished. status [[PXE Server (Open)]] [#p74ace39] ** P: We move /etc/passwd then we can not be root. No more even shutdown. [#oaefbc51] *** S: cntl-alt-del and reboot. Then when OS selection, push any arrow. [#v36584e8] 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 [#xf61128d] *** S: solved. "M-x ispell-change-dictionary" and select english [#t33f8f93] *** S: solved. Edit .emacs to add (setq ispell-dictionary "english") [#l1a50648] ** P: How to update the files of remote to the files of local [#lb59159d] *** S: solved. "rsync -avc -e ssh saito@remote:/home/saito/book09/ /rsaito/book09"[#f25e1654]