Linux SysAdmin Guide

Installing Linux
User Administration [ adduser, removing users. locking accounts ]
Basic Networking
NFS
NIS
Web Server Admin [ installing apache ]
Mail Administration
NT - Linux Networking
ftp Administration

I. Installing Linux

a. Installation

Insert CD and hit DEL to make it the default booting device. Boot from installation CD.

b. Boot Problems

`Unexpected Inconsistency : Run fsck manually' [ Thu. 8/6/01 ]
- #fsck -r / (repair filesystem)
  #exit (auto reboot follows)

c. Hostname

hostname
- #hostname mars (set hostname)
- #hostname (show hostname)
- #uname -a (all host info)
- #uname -n (show hostname)

II. User Administration

a. Adding and Removing Users

useradd (`add new user')
- Options
- Examples
  - #useradd -c "Dr. Samar Abbas" -d /users/samar samar
    #passwd samar (add user samar, setting his password, also possible to use adduser )
  - #adduser -d /users/samar samar; passwd samar
userdel (`delete user')
- Options
- Examples
  - #userdel -r samar (remove user)

III. Basic Networking

a. Hosts

/etc/hosts : Changes take immediate effect, cf. $telnet gamma

/etc/hosts

127.0.0.1   localhost.localdomain   localhost
10.0.0.9    gamma
10.0.0.11   beta

/etc/hosts.allow
/etc/hosts.allow
ALL: ALL in.telnetd: ALL
/etc/hosts.deny
/etc/hosts.deny
ALL: ALL in.telnetd: ALL

/etc/fstab : Files mounted at boot time.

/etc/fstab

/dev/hda2        /           ext2   defaults 1 1
alpha:/cdrom     /cdrom      ignore 0 0 0
/dev/fd0         /mnt/floppy ext2   noauto 0 0
/dev/hda4        /users      ext2   defaults 1 2
10.0.0.6:/abbas  /abbas      nfs    defaults

IV. NFS

a. NFS Server

Configuration Files : /etc/exports, /etc/hosts.allow, /etc/hosts.deny
/etc/exports
/usr/local 199.100.11.5(ro) /home 198.100.12.6(rw)
Starting Services : Check which ones are already running using %rpcinfo -p .
1. Portmapper Start : %rpc.portmap
2. Mount Daemon Start : %rpc.mountd
3. NFS Server Daemon Start : %rpc.nfsd
4. Auxiliary NFS Services : %rpc.statd ; %rpc.lockd ; %rpc.rquotad
  - %rpcinfo -p (at least three lines containing "portmapper", "nfs", and "mountd" should be seen; at most these plus "rquotad", "status", "nlockmgr")
5. Export exports file : %exportfs -ra (force nfsd to re-read /etc/exports)
  b. NFS Client
  - Mount the files :
    - %mount -o rsize=1024,wsize=1024 -t nfs mars:/home/user /home/user (mount, setting default datagram size in muliples of 1024 up to 8192 with mostly 4096 default and specifying nfs file type)
    - %mount mars:/home/user /home/user
    - Check the mount using %df or %mount; NIS setup enables user to see his files.
    - "Type Mismatch" : client or server does not cotain `nfs' in /proc/filesystems; kernel must be rebuilt.
    - "RPC Failure" : nfsd not running on server.
    - "Permission Denied" : Client not in /etc/exports.
  - Unmount the files :
    - %umount /home/user
  V. NIS
  a. NIS Server
  - Start the NIS Server : %ypserv
    - %rpcinfo -u localhost ypserv ( check whether the above worked; one should see the word `running')
  - Build and Install NIS Databases : %/usr/lib/yp/ypinit -m ( takes some time )
    - "Domain Name No Set" : if this is the error message then type %domainname xyz.com
  b. NIS Client
  - Start the NIS Client : %/sbin/ypbind
    - "No NIS Server" : if this is the error message then edit /etc/yp.conf to include a line ypserver mars , where mars must be in /etc/hosts.
    - "No NIS Domain" : if this is the error message then type %domainname xyz.com.
    - %rpcinfo -u localhost ypbind or %rpcinfo -p localhost ( check whether ypbind is running)
    - %ypcat passwd.byname ( check whether the above worked, remote users should be able to login )
  - Mount NFS Files : %mount -o rsize=1024,wsize=1024 -t nfs mars:/home/user /home/user ( mount user's home directory, the user can now view and edit his files )
  VI. Web Server Administration
  a. Installing Apache : Not required for many versions of Linux as Apache is usually preinstaled.
  1. Download
    - $lynx http://www.apache.org/dist/httpd/httpd-2_0_NN.tar.gz (also via http://www.apache.org/dist/httpd/)
  2. Extract
    - $gzip -d httpd-2_0_NN.tar.gz $ tar xvf httpd-2_0_NN.tar (gunzip and untar )
  3. Configure
    - $./configure     ( configure using default options)
      $./configure --help     (get help)
      $./configure --prefix=PREFIX     ( PREFIX defaults to /usr/local/apache2)
```
 $ CC="pgcc" CFLAGS="-O2" \
    ./configure --prefix=/sw/pkg/apache \
    --enable-rewrite=shared \
    --enable-speling=shared  
```
      (specifying C compiler and install dir)
  4. Build
    - $make (compile and build, takes 3 minutes or more )
  5. Install
    - $make install (compile and build, takes 3 minutes or more )
  6. Customize
    - $vi PREFIX/conf/httpd.conf (edit file )
  7. Run
    - $PREFIX/bin/apachectl start (run, test first http://localhost; document root tree is PREFIX/htdocs/)
    - $PREFIX/bin/apachectl stop (stop)
    b. Running Apache
    1. Check Config File
      - /etc/httpd/conf/httpd.conf (should contain an uncommented line ServerName localhost )
    2. Start Apache
      - httpd (start daemon)
      - /usr/sbin/httpd -C "ServerName mars" (start daemon specifying server name)
    3. Test Apache
      - $lynx http://localhost (test server, file displayed is /var/www/html/index.html with /var/www/ as base)
      - $lynx http://mars/ (test servername aliasing)
      c. CGI
      - $lynx http://localhost/cgi-bin/test.cgi (using in-built test script /var/www/cgi-bin/test.cgi and #mv test-cgi test.cgi )
      VII. Mail Admin
      a. sendmail
      - /etc/aliases :
        
        /etc/aliases
        
        ... all: user, samar, mantu ...
      - /etc/sendmail.cf :
        
        /etc/sendmail.cf
        
        ALL: ALL in.telnetd: ALL
      VIII. NT - Linux Networking
      a. Samba
      
      Enables networking between NT and Linux.
      a. Installing Samba
      1. Configure (Not always required)
        
        $./configure --help (help)
      2. Build Binaries
        
        $make     (create binaries)
        
        $make install     (create binaries; $ make installbin, $make installman separately install binaries and manual pages)
        
        Configuration File smb.conf
        
        Consult examples dir. file
        [global] workgroup = MYGROUP [homes] guest ok = no read only = no
            ( smb.conf should be in same place as spec. in Makefile, default /usr/local/samba/lib/ )
        
        Test smb.conf
        
        $testparm     (test)
        
        smbd and nmbd Daemons started
        
        Possibility 1: Inetd $/etc/inetd.conf     (test)
        
        Possibility 2: Shell Script $mystartsmb.sh
        #!/bin/sh /usr/local/samba/bin/smbd -D /usr/local/samba/bin/nmbd -D
        $chmod 755 *.sh; ./startsmb.sh     (executable run by hand or exec by /etc/rc.local )
        
        Test Connections
        
        $ smbclient -L yourhostname     (get list of host names)
        
        $ smbclient //yourhostname/aservice     (connect with linux client)
        
        C:\WINDOWS\> net use d: \\servername\service     (try mounting disks)
        
        a. Features of Samba
        
        Config Files
        
        $smb.conf     (similar to ini files, manipulatable via $swat
        
        Other tools include qmail, fetchmail, mgetty, sendfax and hylafax.