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How to change UID and GID? chown

UID = User ID
GID = Group ID

We can change UID and GID with command ‘chown’ login with SSH.

chown -R newuserID:newgroupID folder_name

For example, to change myfolder UID and GID

chown -R bdhostit:bdhostit myfolder

or to change maildir UID and GID. Here, “bdhostit” is account’s username.

chown -R bdhostit:mail /home/bdhostit/domains/Maildir

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Linux fstab File and how it works | Understanding fstab file system

Fstab is file system table your operating system. fstab file location:

/etc/fstab

In a Linux-based system, /etc/fstab file is one of the most important files. It contains all available disks, disk partitions and their options. You can open and see your fstab file system as follows

vi /etc/fstab

Check mount information of partition /dev/sdb1

lsblk -d -fs /dev/sdb1

If you add new hard disk or repartition an existing one, you’ll have to modify this file. And for every partition has been described on a separate line and each line contains six fields which provide information about its mount.

  1. Device is the first field represents disk or partition name. Most distributions specify partitions by their labels or UUIDs. 
    /dev/sda1

    or

    80b496fa-ce2d-4dcf-9afc-bcaa731a67f1
  2. Mount point is the second field represents directory where the partition or disk will be mounted. And the directory should be an empty directory. 
    /backup
  3. File system type the third field represents the file system type. 
    ext4
  4. Options is the fourth field represents the mount options. Here, we will use default options. Default mount options sets are:
    • rw (read-write);
    • suid (respect setuid and setgid bits);
    • dev (interpret characters and block devices on the filesystem);
    • exec (allow executing binaries and scripts);
    • auto (mount the filesystem when the -a option of the mount command is used);
    • nouser (make the filesystem not mountable by a standard user);
    • async (perform I/O operations on the filesystem asynchronously). 
      defaults
  5. Backup operation is the fifth field and can be either 0 or 1. ‘1’, if the dump utility should back up a partition and ‘0’, if it shouldn’t. 
    1
  6. File system check order is the sixth field represents fsck checks order for device/partition errors at boot time. ‘0’ means that fsck should not check file system. Higher numbers represent the check order. The root partition have value ‘1’ and all others should have value from 2. 
    2

Check mount information of partition /dev/sdb1

lsblk -d -fs /dev/sdb1

 

 

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View Directory Tree Structure In Linux

Install directory tree to see directory structure in linux, if not installed previously.

sudo yum install tree
  • Run the tree command without any arguments 
    tree
  • View all directories 
    tree -L 1 /

    here, L indicates maximum depth of displaying directory tree

  • List the files of the specific directory 
    tree /home
  • To list hidden files of etc directory 
    tree -a /etc
  • To view list in color format 
    tree -C /etc
  • List only the directories using -d parameter 
    tree -d /home

 

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Linux File Permissions | chmod command in numeric mode | chown

  • View directory permission with ls command. 
    ls -l dirName
  • View file permission with ls command. 
    ls -l fileName
  • Some examples of how to use the chmod command in numeric mode: 
    chmod 644 fileName
  • To recursively operate on all files and directories under the given directory, use the -R option: 
    chmod -R 755 dirName
  • Recursive file own 
    chown -R vmail:vmail /var/vmail