Linux
- How to verify that SSL for IMAP/SMTP works and a proper SSL certificate is in use
- Get Numeric File/Directory Permissions
- Mount SMB Share in fstab Ubuntu
- Find out what's taking up all the space in your linux install
- Extract Certificate Information with OpenSSL
- Run fstrim manually
How to verify that SSL for IMAP/SMTP works and a proper SSL certificate is in use
Credit Robert Asibekov
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:
644Mount 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 </dev/null | openssl x509 -outform pem > googlecert.pemDecode the Entire Certificate
openssl x509 -in googlecert.pem -noout -textExtract Specific Information from the Certificate
Extract the Subject
openssl x509 -in googlecert.pem -noout -subject subject=CN = *.google.comExtract the Issuer
$ openssl x509 -in googlecert.pem -noout -issuer issuer=C = US, O = Google Trust Services LLC, CN = GTS CA 1C3Extracting 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