# Linux # How to verify that SSL for IMAP/SMTP works and a proper SSL certificate is in use

Credit [Robert Asibekov](https://support.plesk.com/hc/en-us/articles/213961665-How-to-verify-that-SSL-for-IMAP-POP3-SMTP-works-and-a-proper-SSL-certificate-is-in-use)

#### IMAP via SSL using port 993 - connect to a mail server using openssl: ``` openssl s_client -showcerts -connect mail.example.com:993 -servername mail.example.com ``` - Check output and make sure that a valid certificate is shown: ``` Server certificate subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.example.com issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 ``` - Make sure that you received IMAP server response: ``` * OK [CAPABILITY IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA AUTH=CRAM-MD5 AUTH=PLAIN IDLE ACL ACL2=UNION] Courier-IMAP ready. Copyright 1998-2004 Double Precision, Inc. See COPYING for distribution information. ``` #### SMTP via TLS/StartTLS using port 25 or 587 - Connect to a mail server using openssl: ``` openssl s_client -starttls smtp -showcerts -connect mail.example.com:25 -servername mail.example.com ``` - Check output and make sure that a valid certificate is shown: ``` Server certificate subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.example.com issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=PositiveSSL CA 2 ``` - Make sure that you received SMTP server response: ``` 250 DSN ``` # Get Numeric File/Directory Permissions - Run the following command as root on a file/directory of your choice: ``` stat -c %a /etc/hosts ``` - You should get the numeric permissions of the file/directory output: ``` 644 ``` # Mount SMB Share in fstab Ubuntu #### Username/Password in connect string - Edit /etc/fstab: ``` vi /etc/fstab ``` - Enter the following: ``` #theShare //theServer/theShare /mnt/theMount cifs vers=3.0,username=theUsername,password=thePassword,uid=1000,gid=104,iocharset=utf8,file_mode=0777,dir_mode=0777,nounix 0 0 ``` #### Username/Password in credentials file - Create a credentials file to a directory of your choice: ``` vi /home/username/.smbcredentials ``` - Enter the following entries and adjust the username, passwore and/or domain to your environment: ``` #username=MyUsername #password=MyPassword # OR: username=MyUsername password=MyPassword domain=MYDOMAIN ``` - Save and set the permissions to the .smbcredentials file to 660: ``` chmod 660 /home/username/.smbcredentials ``` - Edit /etc/fstab: ``` vi /etc/fstab ``` - Enter the following: ``` #theShare //theServer/theShare /mnt/theMount cifs vers=3.0,credentials=/home/username/.smbcredentials,uid=1000,gid=104,iocharset=utf8,file_mode=0777,dir_mode=0777,nounix 0 0 ```
# Find out what's taking up all the space in your linux install ##### Example for / partition: ``` du -h / | grep '[0-9\.]\+G' ``` # Extract Certificate Information with OpenSSL ### Fetch the X.509 Public Key Certificate File ``` openssl s_client -connect google.com:443 -showcerts googlecert.pem ``` ## Decode the Entire Certificate ``` openssl x509 -in googlecert.pem -noout -text ``` ## Extract Specific Information from the Certificate #### Extract the Subject ``` openssl x509 -in googlecert.pem -noout -subject subject=CN = *.google.com ``` #### Extract the Issuer ``` $ openssl x509 -in googlecert.pem -noout -issuer issuer=C = US, O = Google Trust Services LLC, CN = GTS CA 1C3 ``` #### Extracting the Extension Fields ``` $ openssl x509 -in googlecert.pem -noout -ext subjectAltName X509v3 Subject Alternative Name: DNS:*.google.com, DNS:*.appengine.google.com, DNS:*.bdn.dev, DNS:*.cloud.google.com, DNS:*.crowdsource.google.com, DNS:*.datacompute.google.com, ...(truncated) ``` # Run fstrim manually ``` fstrim / -v ``` # Watch for changes in Linux directory Install inotify-tools: ``` apt-get install inotify-tools ``` Watch a directory for changes: ``` inotifywait -m -r /directory/of/your/choice ```