Remote server SSH login without password

SSH login without password

You want to use Linux and OpenSSH to automate your tasks.

Therefore you need an automatic login from host 172.19.7.xyz / user root (user of first server) to Host 172.19.7.acb / user root(user of second server). We don't want to enter any passwords, because we want to call ssh from a within a shell script.

How to do it

First log in on172.19.7.xyz as user root and generate a pair of authentication keys. Do not enter a passphrase:

Server01:~> ssh-keygen -t rsa

Generating public/private rsa key pair.

Enter file in which to save the key (/home/a/.ssh/id_rsa):

Created directory '/home/a/.ssh'.

Enter passphrase (empty for no passphrase):

Enter same passphrase again:

Your identification has been saved in /home/a/.ssh/id_rsa.

Your public key has been saved in /home/a/.ssh/id_rsa.pub.

The key fingerprint is:

3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 a@A

Now use ssh to create a directory ~/.ssh as user root on 172.19.7.abc. (The directory may already exist, which is fine):

Server01:~> ssh root@172.19.7.abc mkdir -p .ssh

Server02's password:

Finally append a's new public key to root@172.19.7.abc:.ssh/authorized_keys and enter Sever02's password one last time:

Server01:~> cat .ssh/id_rsa.pub | ssh root@172.19.7.abc 'cat >> .ssh/authorized_keys'

Server02's password:

From now on you can log into 172.19.7.abc as root from 172.19.7.xyz as a without password:

Server01:~> ssh root@172.19.7.abc

A note from one of our readers: Depending on your version of SSH you might also have to do the following changes:

Put the public key in .ssh/authorized_keys2

Change the permissions of .ssh to 700

Change the permissions of .ssh/authorized_keys2 to 640

how to set Disk Quota:- This example shows to set it at /home.

[root@localhost ~]# vi /etc/fstab

 [root@localhost ~]# cat /etc/fstab

#

# /etc/fstab

# Created by anaconda on Wed Aug  6 22:20:17 2014

#

# Accessible filesystems, by reference, are maintained under '/dev/disk'

# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info

#

UUID=0bb45273-d0fc-4329-95cf-e3570ccfd7f3 /                       ext4    defaults        1 1

UUID=6f7c1a9e-2c79-473d-b0ed-ca2bd1e32157 /boot                   ext4    defaults        1 2

UUID=9d064cb9-23f2-4e37-9224-0355159f1fc4 /home                   ext4    defaults,usrquota    1 2

UUID=dfdb72be-04a8-4d35-aa70-1716ef66fb50 swap                    swap    defaults        0 0

tmpfs                   /dev/shm                tmpfs   defaults        0 0

devpts                  /dev/pts                devpts  gid=5,mode=620  0 0

sysfs                   /sys                    sysfs   defaults        0 0

proc                    /proc                   proc    defaults        0 0

 [root@localhost ~]#  rpm -qa | grep quota

quota-3.17-18.el6.x86_64

Ø  Although Red Hat supports quotas in the kernel by default but you can verify quota support from the kernel with the following command:

 [root@localhost ~]# grep -i config_quota /boot/config-`uname -r`

CONFIG_QUOTA=y

CONFIG_QUOTA_NETLINK_INTERFACE=y

# CONFIG_QUOTA_DEBUG is not set

CONFIG_QUOTA_TREE=y

CONFIG_QUOTACTL=y

Ø  You now need to remount the /home file system before the changes take effect.

[root@localhost ~]# mount -o remount /home/

 [root@localhost ~]# mount

/dev/vda2 on / type ext4 (rw)

proc on /proc type proc (rw)

sysfs on /sys type sysfs (rw)

devpts on /dev/pts type devpts (rw,gid=5,mode=620)

tmpfs on /dev/shm type tmpfs (rw,rootcontext="system_u:object_r:tmpfs_t:s0")

/dev/vda1 on /boot type ext4 (rw)

/dev/vda5 on /home type ext4 (rw)

none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)

/tmp on /tmp type none (rw,bind)

/var/tmp on /var/tmp type none (rw,bind)

/home on /home type none (rw,usrquota)

none on /sys/kernel/config type configfs (rw)

sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)

gvfs-fuse-daemon on /root/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev)

[root@localhost ~]# quotacheck -um /home  # create quota file

[root@localhost ~]# quotaon -uv /home         # enable disk quota

/dev/vda5 [/home]: user quotas turned on

[root@localhost ~]# quotaon -p –a          #  show status

group quota on /home (/dev/vda5) is off

user quota on /home (/dev/vda5) is on

[root@localhost ~]# useradd ashwini

[root@localhost ~]# passwd ashwini

Changing password for user ashwini.

New password:

BAD PASSWORD: it is based on a dictionary word

BAD PASSWORD: is too simple

Retype new password:

passwd: all authentication tokens updated successfully.

[root@localhost ~]# edquota ashwini                     # set user quota to a user 'ashwini'

 [root@localhost ~]# repquota –a                            # show status

*** Report for user quotas on device /dev/vda5

Block grace time: 7days; Inode grace time: 7days

                        Block limits                File limits

User            used    soft    hard  grace    used  soft  hard  grace

----------------------------------------------------------------------

root      --      20       0       0              2     0     0

xguest    --      36       0       0              9     0     0

ashwini   --    1024   12000000 15000000             20     0     0

 [root@localhost ~]# useradd desiree

[root@localhost ~]# passwd desiree

Changing password for user desiree.

New password:

BAD PASSWORD: it is based on a dictionary word

BAD PASSWORD: is too simple

Retype new password:

passwd: all authentication tokens updated successfully.

[root@localhost ~]# edquota desiree     # set user quota to a user 'ashwini'

[root@localhost ~]# repquota –a             # show status

*** Report for user quotas on device /dev/vda5

Block grace time: 7days; Inode grace time: 7days

                        Block limits                File limits

User            used    soft    hard  grace    used  soft  hard  grace

----------------------------------------------------------------------

root      --      20       0       0              2     0     0

xguest    --      36       0       0              9     0     0

ashwini   --    5148   12000000 15000000             20     0     0

desiree   --      48   12000000 15000000             12     0     0

[root@localhost ~]# useradd mohan

[root@localhost ~]# passwd mohan

Changing password for user mohan.

New password:

BAD PASSWORD: it is based on a dictionary word

BAD PASSWORD: is too simple

Retype new password:

passwd: all authentication tokens updated successfully.

[root@localhost ~]# edquota mohan      # set user quota to a user ' mohan '

[root@localhost ~]# repquota –a             # show status

*** Report for user quotas on device /dev/vda5

Block grace time: 7days; Inode grace time: 7days

                        Block limits                File limits

User            used    soft    hard  grace    used  soft  hard  grace

----------------------------------------------------------------------

root      --      20       0       0              2     0     0

xguest    --      36       0       0              9     0     0

ashwini   --    5148  12000000 15000000            20     0     0

desiree   --      48  12000000 15000000             12     0     0

mohan     --      48   12000000 15000000            12     0     0

[root@localhost ~]# useradd devraj

 [root@localhost ~]# passwd devraj

Changing password for user devraj.

New password:

BAD PASSWORD: it is based on a dictionary word

BAD PASSWORD: is too simple

Retype new password:

passwd: all authentication tokens updated successfully.

[root@localhost ~]# edquota devraj       # set user quota to a user ' devraj '

[root@localhost ~]# repquota –a             # show status

*** Report for user quotas on device /dev/vda5

Block grace time: 7days; Inode grace time: 7days

                        Block limits                File limits

User            used    soft    hard  grace    used  soft  hard  grace

----------------------------------------------------------------------

root      --      20       0       0              2     0     0

xguest    --      36       0       0              9     0     0

ashwini   --    5148   12000000 15000000            20     0     0

desiree   --      48   12000000 15000000           12     0     0

mohan     --      48   12000000 15000000             12     0     0

devraj    --      48   12000000 15000000             12     0     0

[root@localhost ~]# useradd sriram

[root@localhost ~]# passwd sriram

Changing password for user sriram.

New password:

BAD PASSWORD: it is based on a dictionary word

BAD PASSWORD: is too simple

Retype new password:

passwd: all authentication tokens updated successfully.

[root@localhost ~]# edquota sriram                       # set user quota to a user ' sriram  '

[root@localhost ~]# repquota –a                             # show status

*** Report for user quotas on device /dev/vda5

Block grace time: 7days; Inode grace time: 7days

                        Block limits                File limits

User            used    soft    hard  grace    used  soft  hard  grace

----------------------------------------------------------------------

root      --      20       0       0              2     0     0

xguest    --      36       0       0              9     0     0

ashwini   --    5148  12000000 15000000            20     0     0

desiree   --      48  12000000 15000000             12     0     0

mohan     --      48   12000000 15000000            12     0     0

devraj    --      48   12000000 15000000             12     0     0

sriram    --      48   12000000 15000000             12     0     0





Note: 1 Block size is 4kb(4096) it's depends on file system size. 

Here 15000000 KB is 15GB and 12000000KB= 12GB