wanip-checker/ssmtp_conf-sample

sSMTP system pre-configuration

Once you have installed sSMTP on your Linux system, make sure the following applies. Run these configuration commands as root or with sudo.

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1) Check that symbolic link from /usr/bin/ssmtp to /usr/bin/sendmail exists:

ln -s /usr/bin/ssmtp /usr/bin/sendmail

Test:

> stat -c "%A %a %U:%G %N" /usr/bin/sendmail
lrwxrwxrwx 777 root:root /usr/bin/sendmail -> ssmtp

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NOTE: User & group mail are defined on Arch Linux by default, preinstalled with filesystem package. If they do not exist, then do the following.

2) Make sure user & group mail exists, and directory /var/spool/mail exists with proper permissions:

mkdir -p /var/spool/mail
chmod 1777 /var/spool/mail
groupadd -g 12 mail
useradd -r -d /var/spool/mail -s /sbin/nologin -u 12 -g 12 mail

Test:

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> sudo stat -c "%A %a %U:%G %n" /var/spool/mail
drwxrwxrwt 1777 root:root /var/spool/mail
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> grep mail /etc/passwd
mail:x:12:12::/var/spool/mail:/sbin/nologin
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> grep mail /etc/group
mail:x:12:

sSMTP configuration files

Once you have sSMTP installed on your Linux system, configure ssmtp.conf and revaliases in /etc/ssmtp/ folder.

Mail message formatting & email address

Configure your message defined in wanchecker.sh file.

wanchecker.sh variables:

Variable	Value	Type
SUBJECT_EMAIL	Email title	String
MESSAGE_EMAIL	Email message contents	String
MESSAGE_STDOUT	Internal Linux system message about sent email message	String
WANIP_DIR	Log file directory path. User mail must have write access to this folder.	String
WANIP_LOG	Log file name	String

Mail sender and recipients

These are found in /etc/ssmtp/wanchecker.conf which is a bash source file. The conf file has three variables: ENABLE_FALLBACK_DNS, EMAIL_SENDER and EMAIL_RECIPIENTS which must be configured. EMAIL_SENDER takes same value as defined in /etc/ssmtp/ssmtp.conf (sample) and /etc/ssmtp/revaliases (sample) files.

Folder & file permissions

Permissions for /etc/ssmtp folder should be:

> stat -c "%A %a %U:%G %n" /etc/ssmtp
drwxr-x--- 750 root:mail /etc/ssmtp

Contents of /etc/ssmtp/ folder should contain the following files & permissions:

> stat -c "%A %a %U:%G %n" /etc/ssmtp/*
-rw-r----- 640 root:mail /etc/ssmtp/revaliases
-rw-r----- 640 root:mail /etc/ssmtp/ssmtp.conf
-rwxr-x--- 750 root:mail /etc/ssmtp/wanchecker.sh
-rwxr-x--- 640 root:mail /etc/ssmtp/wanchecker.conf

NOTE: As /etc/ssmtp/ssmtp.conf contains a clear-text email password, the file must be protected from any eavesdropping with correct permission policy! The file must not be readable to any other than mail user, and mail user must not be available for normal usage. Still, any sudo group member can access the file, so make sure sudo group does not contain hostile or unwanted members, and configure your /etc/sudoers file properly.