source: server/other/openssh.xml@ 1b83a7c1

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
   "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../../general.ent">
  %general-entities;

<!ENTITY openssh-download-http "http://sunsite.ualberta.ca/pub/OpenBSD/OpenSSH/portable/openssh-&openssh-version;.tar.gz">
<!ENTITY openssh-download-ftp "ftp://ftp.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-&openssh-version;.tar.gz">
<!ENTITY openssh-md5sum "7b36f28fc16e1b7f4ba3c1dca191ac92">
<!ENTITY openssh-size "889 KB">
<!ENTITY openssh-buildsize "14.5 MB">
<!ENTITY openssh-time "0.42 SBU">
]>

<sect1 id="openssh" xreflabel="OpenSSH-&openssh-version;">
<sect1info>
<othername>$LastChangedBy$</othername>
<date>$Date$</date>
</sect1info>
<?dbhtml filename="openssh.html"?>
<title>Open<acronym>SSH</acronym>-&openssh-version;</title>
<indexterm zone="openssh">
<primary sortas="a-OpenSSH">OpenSSH</primary></indexterm>

<sect2>
<title>Introduction to 
<application>Open<acronym>SSH</acronym></application></title>

<para>The <application>Open<acronym>SSH</acronym></application> package 
contains <command>ssh</command> clients and the <command>sshd</command> daemon. 
This is useful for encrypting authentication and subsequent traffic over a 
network.</para>

<sect3><title>Package information</title>
<itemizedlist spacing='compact'>
<listitem><para>Download (HTTP): 
<ulink url="&openssh-download-http;"/></para></listitem>
<listitem><para>Download (FTP): 
<ulink url="&openssh-download-ftp;"/></para></listitem>
<listitem><para>Download MD5 sum: &openssh-md5sum;</para></listitem>
<listitem><para>Download size: &openssh-size;</para></listitem>
<listitem><para>Estimated disk space required: 
&openssh-buildsize;</para></listitem>
<listitem><para>Estimated build time: 
&openssh-time;</para></listitem></itemizedlist>
</sect3>

<sect3><title><application>Open<acronym>SSH</acronym></application> 
dependencies</title>
<sect4><title>Required</title>
<para><xref linkend="openssl"/></para>
</sect4>

<sect4><title>Optional</title>
<para><xref linkend="Linux_PAM"/>, 
<xref linkend="tcpwrappers"/>, 
X (<xref linkend="xfree86"/> or <xref linkend="xorg"/>), 
<xref linkend="mitkrb"/> or <xref linkend="heimdal"/>, 
<xref linkend="j2sdk"/>, 
<xref linkend="net-tools"/>, 
<ulink url="http://www.opensc.org/">OpenSC</ulink> and 
<ulink url="http://sourceforge.net/projects/libedit/">libedit</ulink></para>
</sect4>
</sect3>

</sect2>

<sect2>
<title>Installation of 
<application>Open<acronym>SSH</acronym></application></title>

<para><application>Open<acronym>SSH</acronym></application> runs as two 
processes when connecting to other computers. The first process is a 
privileged process and controls the issuance of privileges as necessary. 
The second process communicates with the network. Additional installation 
steps are necessary to set up the proper environment, which are performed 
by the following commands:</para>

<screen><userinput><command>install -v -d -m700 /var/lib/sshd &amp;&amp;
chown root:sys /var/lib/sshd &amp;&amp;
groupadd sshd &amp;&amp;
useradd -c 'sshd PrivSep' -d /var/lib/sshd -g sshd -s /bin/false sshd</command></userinput></screen>

<para><application>OpenSSH</application> is very sensitive to changes in the
linked <application>OpenSSL</application> libraries. If you recompile
<application>OpenSSL</application>, <application>OpenSSH</application> may
fail to startup. An alternative is to link against the static 
<application>OpenSSL</application> library. To link against the static 
library, execute the following command:</para>

<screen><userinput><command>sed -i "s:-lcrypto:/usr/lib/libcrypto.a:g" configure</command></userinput></screen>

<para>Install <application>Open<acronym>SSH</acronym></application> by running 
the following commands:</para>

<screen><userinput><command>./configure --prefix=/usr --sysconfdir=/etc/ssh \
    --libexecdir=/usr/sbin --with-md5-passwords \
    --with-privsep-path=/var/lib/sshd</command></userinput></screen>

<para>If you use <application>Heimdal</application> as your Kerberos5 
implementation and you linked the <application>Heimdal</application> libraries 
into the build using the <option>--with-kerberos5</option> parameter, you'll 
need to modify the <filename>Makefile</filename> or the build will fail. Use 
the following command:</para>

<screen><userinput><command>sed -i -e "s/lkrb5 -ldes/lkrb5/" Makefile</command></userinput></screen>

<para>Continue the build:</para>

<screen><userinput><command>make</command></userinput></screen>

<para>If you linked <application>tcp_wrappers</application> into the build 
using the <option>--with-tcp-wrappers</option> parameter, ensure you add 
127.0.0.1 to the sshd line in <filename>/etc/hosts.allow</filename> if you 
have a restrictive <filename>/etc/hosts.deny</filename> file, or the testsuite 
will fail. To run the testsuite, issue: <command>make -k 
tests</command>.</para>

<para>Now, as the root user:</para>

<screen><userinput role='root'><command>make install</command></userinput></screen>

</sect2>

<sect2>
<title>Command explanations</title>

<para><parameter>--sysconfdir=/etc/ssh</parameter>: This prevents the 
configuration files from being installed in 
<filename class="directory">/usr/etc</filename>.</para>

<para><parameter>--with-md5-passwords</parameter>: This is required
if you made the changes recommended by the shadowpasswd_plus
<acronym>LFS</acronym> hint on
your <acronym>SSH</acronym> server when you installed the Shadow Password 
Suite or if you access a <acronym>SSH</acronym> server that authenticates by 
user passwords encrypted with md5. </para>

<para><parameter>--libexecdir=/usr/sbin</parameter>: This parameter 
changes the installation path of some programs to 
<filename class="directory">/usr/sbin</filename> instead of 
<filename class="directory">/usr/libexec</filename>.</para>

</sect2>

<sect2>
<title>Configuring <application>Open<acronym>SSH</acronym></application></title>

<sect3 id="openssh-config"><title>Config files</title>

<para><filename>~/.ssh/*, /etc/ssh/ssh_config</filename> and 
<filename>/etc/ssh/sshd_config</filename></para>
<indexterm zone="openssh openssh-config">
<primary sortas="e-AA.ssh">~/.ssh/*</primary></indexterm>
<indexterm zone="openssh openssh-config">
<primary sortas="e-etc-ssh-ssh_config">/etc/ssh/ssh_config</primary>
</indexterm>
<indexterm zone="openssh openssh-config">
<primary sortas="e-etc-ssh-sshd_config">/etc/ssh/sshd_config</primary>
</indexterm>

<para>There are no required changes to any of these files. However,  
you may wish to view the <filename class='directory'>/etc/ssh/</filename> to 
make changes for appropriate security of your system. One recomended change 
is that you disable root login via <command>ssh</command>. Execute the 
following command to disable root login via <command>ssh</command>:</para>

<screen><userinput><command>echo "PermitRootLogin no" >> /etc/ssh/sshd_config</command></userinput></screen>

<para>Additional configuration information can be found in the man pages for
<command>sshd</command>, <command>ssh</command> and 
<command>ssh-agent</command>.</para>
</sect3>

<sect3 id="openssh-init"><title>sshd init.d script</title>

<para>To start the <acronym>SSH</acronym> server at system boot, install the 
<filename>/etc/rc.d/init.d/sshd</filename> init script included in the 
<xref linkend="intro-important-bootscripts"/> package.</para>
<indexterm zone="openssh openssh-init">
<primary sortas="f-sshd">sshd</primary></indexterm>

<screen><userinput><command>make install-sshd</command></userinput></screen>
</sect3>

</sect2>

<sect2>
<title>Contents</title>

<segmentedlist>
<segtitle>Installed Programs</segtitle>
<segtitle>Installed Libraries</segtitle>
<segtitle>Installed Directories</segtitle>

<seglistitem>
<seg>scp, sftp, sftp-server, slogin, ssh, sshd, ssh-add, ssh-agent, 
ssh-keygen, ssh-keyscan and ssh-keysign</seg>
<seg>None</seg>
<seg>/etc/ssh and /var/lib/sshd</seg>
</seglistitem>
</segmentedlist>

<variablelist>
<bridgehead renderas="sect3">Short Descriptions</bridgehead>
<?dbfo list-presentation="list"?>

<varlistentry id="scp">
<term><command>scp</command></term>
<listitem><para>is a file copy program that acts like <command>rcp</command> 
except it uses an encrypted protocol.</para>
<indexterm zone="openssh scp">
<primary sortas="b-scp">scp</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="sftp">
<term><command>sftp</command></term>
<listitem><para>is an <acronym>FTP</acronym>-like program that works over 
<acronym>SSH</acronym>1 and <acronym>SSH</acronym>2 protocols.</para>
<indexterm zone="openssh sftp">
<primary sortas="b-sftp">sftp</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="sftp-server">
<term><command>sftp-server</command></term>
<listitem><para>is an <acronym>SFTP</acronym> server subsystem.</para>
<indexterm zone="openssh sftp-server">
<primary sortas="b-sftp-server">sftp-server</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="slogin">
<term><command>slogin</command></term>
<listitem><para>is a symlink to <command>ssh</command>.</para>
<indexterm zone="openssh slogin">
<primary sortas="g-slogin">slogin</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="ssh">
<term><command>ssh</command></term>
<listitem><para>is an <command>rlogin</command>/<command>rsh</command>-like 
client program except it uses an encrypted protocol.</para>
<indexterm zone="openssh ssh">
<primary sortas="b-ssh">ssh</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="sshd">
<term><command>sshd</command></term>
<listitem><para>is a daemon that listens for <command>ssh</command> login 
requests.</para>
<indexterm zone="openssh sshd">
<primary sortas="b-sshd">sshd</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="ssh-add">
<term><command>ssh-add</command></term>
<listitem><para>is a tool which adds keys to the 
<command>ssh-agent</command>.</para>
<indexterm zone="openssh ssh-add">
<primary sortas="b-ssh-add">ssh-add</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="ssh-agent">
<term><command>ssh-agent</command></term>
<listitem><para>is an authentication agent that can store private keys.</para>
<indexterm zone="openssh ssh-agent">
<primary sortas="b-ssh-agent">ssh-agent</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="ssh-keygen">
<term><command>ssh-keygen</command></term>
<listitem><para>is a key generation tool.</para>
<indexterm zone="openssh ssh-keygen">
<primary sortas="b-ssh-keygen">ssh-keygen</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="ssh-keyscan">
<term><command>ssh-keyscan</command></term>
<listitem><para>is a utility for gathering public host keys from a number of 
hosts.</para>
<indexterm zone="openssh ssh-keyscan">
<primary sortas="b-ssh-keyscan">ssh-keyscan</primary>
</indexterm></listitem>
</varlistentry>

<varlistentry id="ssh-keysign">
<term><command>ssh-keysign</command></term>
<listitem><para>is used by <command>ssh</command> to access the local host 
keys and generate the digital signature required during hostbased 
authentication with <acronym>SSH</acronym> protocol version 2.</para>
<indexterm zone="openssh ssh-keysign">
<primary sortas="b-ssh-keysign">ssh-keysign</primary>
</indexterm></listitem>
</varlistentry>
</variablelist>

</sect2>

</sect1>