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

P = problem;
S = solution


** P: (2018.08.07) New Windows 10 cannot access Samba server [#g0cc2a5b]

*** S: Check this answer: [#dd29725f]

** P: (2016.03.10) A new FLEX user cannot receive e-mail. [#k2861b15]

*** S: Don't forget to restart dovecot and postfix after creating the user [#m70339cb]
 $ sudo service dovecot restart
 $ sudo service postfix restart

** P: (2015.08.06) Sometimes CPU RAM disc is occupied by unused memory and it isn't deleted or moved automatically. (Particularly in the case we calculated by Quantum espresso in local disc.) [#jdc235c1]

*** S: We can free up by following command. [#l5bf5994]
We can check our current memory usage using this command:
 $ watch -n 1 free -m
 $ watch -n 1 cat /proc/meminfo
We can free up unused memory under Ubuntu/Linux Mint using this command:
 $ sudo sysctl -w vm.drop_caches=3
 $ sudo sync && echo 3 | sudo tee /proc/sys/vm/drop_caches
Please check this site, too:

** P: (2014.10.17) SSH Error with GSSAPI unsupported options [#dcdad085]
When we login to TUBE systems, the following message appears:
 /etc/ssh/ssh_config line 53: Unsupported option "gssapiauthentication"
 /etc/ssh/ssh_config line 54: Unsupported option "gssapidelegatecredentials"

*** S: Modify /etc/ssh/ssh_config of FLEX [#aa42db8a]
Give comment sign to the following lines (or remove them completely)
 #    GSSAPIAuthentication yes
 #    GSSAPIDelegateCredentials no
Try again to login to TUBE systems.

** P: (2014.10.14) HTML helper mode by emacs does not work for updating the timestamp [#cd3ed372]

*** S: The hhmts code should be in one line and with a proper spacing in order for emacs to change the HTML time-stamp automatically. [#y6963d13]

 <!-- hhmts start --> Last modified: Tue Oct 14 16:58:36 JST 2014 <!-- hhmts end  -->
is a CORRECT syntax.

 <!-- hhmts start -->
 Last modified: Tue Oct 14 16:58:36 JST 2014
 <!-- hhmts end -->
is a FALSE syntax.

** P: (2014.8.22) DVI file does not show figures after compiling latex files. [#sd09166d]
*** S: Do not use any additional option in graphicx package [#o987b86d]
- In the past, people usually add:
- In the current latex system, excluding any options is sufficient:

** P: (2014.8.20) Thunderbird connection to flex does not work. [#x6f6c6f9]
*** S: Edit /etc/dovecot/conf.d/20-imap.conf [#ve3be4db]
 mail_max_userip_connections = 10 
and then
 sudo service dovecot restart
** P: (2014.8.19) NFS in new FLEX Ubuntu 14.04 is very slow [#dc220b13]
*** S: This is a known bug for the latest ubuntu. We should fix nfs-common and blacklist kerberos configuration. [#o465c4f7]
- In /etc/default/nfs-common:
should be modified to be
- In /etc/modprobe.d/blacklist.conf add the following line
 # Blacklist rpcsec_gss_krb5 kernel module; needed for quick NFSv4 mounts
 blacklist rpcsec_gss_krb5
- Restart nfs daemon:
 $ sudo service nfs-kernel-server restart

Check also this reference:

** P: (2014.8.18) Samba sever cannot be accessed in the new FLEX (Ubuntu 14.04) [#y2761e31]

*** S: We found that the location of passdb.tdb should be different to the old FLEX [#k99e6bbb]
- In old FLEX, passdb.tdb is put under
- In new FLEX, passdb.tdb should instead be put under
- After putting passdb.tdb in the correct location, don't forget to restart the samba services:
 # sudo service smbd restart
 # sudo service nmbd restart

** P: (2014.8.14) E-mail sent through aliasing system (all, slab, etc) always repeats itself around every half an hour [#tb401f0d]

*** S: Check the routing policy is correct [#n8662d9c]
- Check /etc/hosts is set correctly
- Execute again /root/ on old FLEX and /root/ on new FLEX
- If the problem still exists, restart both old FLEX and new FLEX and execute again above scripts.
- Make sure other computers do not share the same hostname.

** P: (2014.8.13) Evince does not work well on Ubuntu 14.02 [#j6d6a1a5]

*** S: Do the following way[#y4f17e9c]

 sudo ln -s /etc/apparmor.d/usr.bin.evince /etc/apparmor.d/disable 
 sudo /etc/init.d/apparmor restart 

 and add
 export NO_AT_BRIDGE=1
 to /etc/environment

** P: (2014.8.13) How to change mouse focusing policy. [#td824c72]

*** S: System --> Preferences --> Window then find a panel "Behaviour" and click: "Select windows when the mouse moves over them" [#p7f69563]

** P: (2014.8.13) How to change desktop language [#je602ad6]

*** S: - for all users: edit /etc/default/locale and add: [#w3261038]
 LANG = "ja_JP.UTF-8" 
I've done this for new FLEX - for a particular user (corresponding user should do by himself): edit ~/.dmrc and add under [Desktop] section:  
(If we want English, just change above line by

** P: How to zip-file in win8.1 with password which is compatible with all users unzip programs: [#n48b5a05]

*** S: Download and install 7-zip[#w6e3f853]
  1. Download the 7-zip installer for your computer from  Run the program and install 7-zip to your computer.
  2. Choosing your files.
  3. Right-click on items and choosing 7-Zip, then Add to archive.
  4. choose your format from Archive format `zip`.
  5. Enter password.
  6. Finally, OK to create the compressed archive.

** P: (2014.08.04) FLEX can be accessed from Xlaunch (local), but global component such as website and e-mail seem doesn't work [#iptable]
*** S: If you have such a symptom, probably iptable was accidentally modified. We should recover the routing rule to a normal way. [#iptablesol]
- Run the following script:
 $ sudo /root/
** P: (2014.07.24) Xming is no longer good for Windows 8.1 [#xming]
*** S: Install Vcxsrv, which is a clone of Xming, and remove Xming itself. [#xmingsol]
- Download Vcxsrv from the following: 
- After installation, do these steps:
-- Open Xlaunch.
-- Choose "One large window" and press Next.
-- Select "Open sesson via xdmcp" and press Next.
-- Connect to host: and press Next.
-- Give the following additional parameters for Vcxsrv:
 -from <your_working_ip_address>
for example (please change the address, the following is Nugraha's example):
-- Push Next button, Save Configuration, and Finish.

** P: (2014.01.17) NIS in tube 60 does not work, although NFS works [#f406f2e1]
*** S: Activate ypbind with the following command [#ud86344d]
 # sysv-rc-conf ypbind on 
 # reboot
** P: (2013.10.24) X-windows does not work, cannot connect to Flex using X-windows (Xming, NX, etc.) [#ad84a9d5]
*** S: restart X-windows service in Flex [#lbe3cf63]

 #sudo service lightdm restart
** P:(2013.08.26) E-mail does not work after shutting down the Flex [#k721797e]
*** S: restart dovecot and postfix [#ecca53b8]

 #service dovecot start
 #service dovecot stop
 #service dovecot restart
 #sudo /etc/init.d/postfix restart
** P:(2013.06.05) how to customize GDM login screen [#h77ecb82]
*** S: using ubuntu-tweak [#ha11b2d2]

Install ubuntu-tweak
  #sudo add-apt-repository ppa:tualatrix/ppa
  #sudo apt-get update
  #sudo apt-get install ubuntu-tweak

Launch ubuntu-tweak from terminal and customize the login screen

** P: (2013.06.03) xdvi doesn't put period and comma correctly when reading Japanese documents. [#s135a004]

*** S: Check a tutorial created by other people [#p867b0fd] 

Install xdvi-ja

 # apt-get install xdvik-ja

Font map file:

Do the following:

 # cd /etc/texmf/vfontmap.d/
 # mv
 # mv
 # mv 

Next, check the fc-list the name of the Japanese font to use.

 $ fc-list | grep Takao
 Takao P??,TakaoPMincho:style=Regular
 Takao P????,TakaoPGothic:style=Regular

Add the following lines to a file (create new if not exist) under the directory /etc/texmf/vfontmap.d/

        rml  JIS-H      % ASCII pTeX
        rmlv JIS-V      % ASCII pTeX
        dm   JIS-H      % NTT jTeX
        rml-jis  JIS-H  % ptex-jisfonts

        gbm  JIS-H      % ASCII pTeX
        gbmv JIS-V      % ASCII pTeX
        dg   JIS-H      % NTT jTeX
        gbm-jis  JIS-H  % ptex-jisfonts

Finally, update the registration information of the font

 # update-vfontmap

** P: (2012.10.02) How to remove Ubuntu welcome notes [#m70a5bf7]
Welcome to Ubuntu 11.10 (GNU/Linux 3.0.0-25-generic x86_64)

  * Documentation:

  New release '12.04 LTS' available.
  Run 'do-release-upgrade' to upgrade to it.

  *** System restart required ***

*** S: Please check /etc/update-motd.d/ folder [#l0d990ed]
Then change the permission
  sudo chmod 600 * 
** P: (2012.09.26) Warning: File `Makefile' has modification time 38 s in the future [#ycb06c28]
warning:  Clock skew detected.  Your build may be incomplete. Such warning appears in TUBE50
***S: TUBE50 clock is not synchronized to [#j265a3b5]
- [[Download ntp:]] 
- Configure ntp by folowing [[this step:]] 

** P: (2012.09.25)"yes" command appears every time we restart TUBE50 [#p20120925]
*** S: check file /etc/default/nfs-common [#s20120925]
- before:
- after:
important to note: <space> has meaning to separate the variable in sh script.

** 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    # A stratum 1 server at
 #server     # A stratum 2 server at
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
 19 Jan 16:11:08 ntpdate[23079]: adjust time server offset 0.016601 sec
 [root@tube40 ~]# /usr/sbin/ntpdate -u
 19 Jan 16:11:09 ntpdate[23080]: adjust time server offset 0.015737 sec
 [root@tube40 ~]# /usr/sbin/ntpdate -u
 19 Jan 16:11:13 ntpdate[23081]: adjust time server 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 /tmp/home1
 mount -n /tmp/rsaito



** P: (2010.1.6) /rsaito is not automountd on PXE client. [#m92944ad]

*** S: edit and add flexS:/rsaito information on [#q5d5939e]


** 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

** 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

 ./S28autofs forcerestart

 I also delete in /etc/exports 

 the requests from (nuguraha) (mahabubu)
 and (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]

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