VMware Workstation 10: “Error: Could not open /dev/vmmon: No such file or directory. Please make sure that the kernel module vmmon is loaded.”

Problem

When starting VMware Workstation, the following error is displayed:

Could not open /dev/vmmon: No such file or directory.
Please make sure that the kernel module `vmmon' is loaded.

Also, virtual machines cannot be started.

Solution

“vmmon” is the virtual machine monitor kernel module. You can rebuid it by running:

sudo vmware-modconfig --console --install-all

Sample output:

Stopping VMware services:
   VMware Authentication Daemon                            [  OK  ]
   VM communication interface socket family                [  OK  ]
   Virtual machine communication interface                 [  OK  ]
   Virtual machine monitor                                 [  OK  ]
   Blocking file system                                    [  OK  ]
Using 2.6.x kernel build system.
make: Entering directory `/tmp/modconfig-lea0x8/vmmon-only'
/usr/bin/make -C /lib/modules/2.6.32-504.1.3.el6.x86_64/build/include/.. SUBDIRS=$PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= modules
make[1]: Entering directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/linux/driver.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/linux/driverLog.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/linux/hostif.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/apic.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/comport.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/cpuid.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/hashFunc.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/memtrack.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/phystrack.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/task.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/common/vmx86.o
  CC [M]  /tmp/modconfig-lea0x8/vmmon-only/vmcore/moduleloop.o
  LD [M]  /tmp/modconfig-lea0x8/vmmon-only/vmmon.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /tmp/modconfig-lea0x8/vmmon-only/vmmon.mod.o
  LD [M]  /tmp/modconfig-lea0x8/vmmon-only/vmmon.ko.unsigned
  NO SIGN [M] /tmp/modconfig-lea0x8/vmmon-only/vmmon.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
/usr/bin/make -C $PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= postbuild
make[1]: Entering directory `/tmp/modconfig-lea0x8/vmmon-only'
make[1]: `postbuild' is up to date.
make[1]: Leaving directory `/tmp/modconfig-lea0x8/vmmon-only'
cp -f vmmon.ko ./../vmmon.o
make: Leaving directory `/tmp/modconfig-lea0x8/vmmon-only'
Using 2.6.x kernel build system.
make: Entering directory `/tmp/modconfig-lea0x8/vmnet-only'
/usr/bin/make -C /lib/modules/2.6.32-504.1.3.el6.x86_64/build/include/.. SUBDIRS=$PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= modules
make[1]: Entering directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/driver.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/hub.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/userif.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/netif.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/bridge.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/procfs.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/smac_compat.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/smac.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/vnetEvent.o
  CC [M]  /tmp/modconfig-lea0x8/vmnet-only/vnetUserListener.o
  LD [M]  /tmp/modconfig-lea0x8/vmnet-only/vmnet.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /tmp/modconfig-lea0x8/vmnet-only/vmnet.mod.o
  LD [M]  /tmp/modconfig-lea0x8/vmnet-only/vmnet.ko.unsigned
  NO SIGN [M] /tmp/modconfig-lea0x8/vmnet-only/vmnet.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
/usr/bin/make -C $PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= postbuild
make[1]: Entering directory `/tmp/modconfig-lea0x8/vmnet-only'
make[1]: `postbuild' is up to date.
make[1]: Leaving directory `/tmp/modconfig-lea0x8/vmnet-only'
cp -f vmnet.ko ./../vmnet.o
make: Leaving directory `/tmp/modconfig-lea0x8/vmnet-only'
Using 2.6.x kernel build system.
make: Entering directory `/tmp/modconfig-lea0x8/vmblock-only'
/usr/bin/make -C /lib/modules/2.6.32-504.1.3.el6.x86_64/build/include/.. SUBDIRS=$PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= modules
make[1]: Entering directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/block.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/control.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/dentry.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/file.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/filesystem.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/inode.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/module.o
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/stubs.o
/tmp/modconfig-lea0x8/vmblock-only/linux/control.c: In function âExecuteBlockOpâ:
/tmp/modconfig-lea0x8/vmblock-only/linux/control.c:285: warning: assignment from incompatible pointer type
/tmp/modconfig-lea0x8/vmblock-only/linux/control.c:296: warning: passing argument 1 of âputnameâ from incompatible pointer type
include/linux/fs.h:2185: note: expected âstruct filename *â but argument is of type âchar *â
  CC [M]  /tmp/modconfig-lea0x8/vmblock-only/linux/super.o
  LD [M]  /tmp/modconfig-lea0x8/vmblock-only/vmblock.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /tmp/modconfig-lea0x8/vmblock-only/vmblock.mod.o
  LD [M]  /tmp/modconfig-lea0x8/vmblock-only/vmblock.ko.unsigned
  NO SIGN [M] /tmp/modconfig-lea0x8/vmblock-only/vmblock.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
/usr/bin/make -C $PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= postbuild
make[1]: Entering directory `/tmp/modconfig-lea0x8/vmblock-only'
make[1]: `postbuild' is up to date.
make[1]: Leaving directory `/tmp/modconfig-lea0x8/vmblock-only'
cp -f vmblock.ko ./../vmblock.o
make: Leaving directory `/tmp/modconfig-lea0x8/vmblock-only'
Using 2.6.x kernel build system.
make: Entering directory `/tmp/modconfig-lea0x8/vmci-only'
/usr/bin/make -C /lib/modules/2.6.32-504.1.3.el6.x86_64/build/include/.. SUBDIRS=$PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= modules
make[1]: Entering directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/linux/driver.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/linux/vmciKernelIf.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciContext.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciDatagram.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciDoorbell.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciDriver.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciEvent.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciHashtable.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciQPair.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciQueuePair.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciResource.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/common/vmciRoute.o
  CC [M]  /tmp/modconfig-lea0x8/vmci-only/driverLog.o
  LD [M]  /tmp/modconfig-lea0x8/vmci-only/vmci.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /tmp/modconfig-lea0x8/vmci-only/vmci.mod.o
  LD [M]  /tmp/modconfig-lea0x8/vmci-only/vmci.ko.unsigned
  NO SIGN [M] /tmp/modconfig-lea0x8/vmci-only/vmci.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
/usr/bin/make -C $PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= postbuild
make[1]: Entering directory `/tmp/modconfig-lea0x8/vmci-only'
make[1]: `postbuild' is up to date.
make[1]: Leaving directory `/tmp/modconfig-lea0x8/vmci-only'
cp -f vmci.ko ./../vmci.o
make: Leaving directory `/tmp/modconfig-lea0x8/vmci-only'
Using 2.6.x kernel build system.
make: Entering directory `/tmp/modconfig-lea0x8/vsock-only'
/usr/bin/make -C /lib/modules/2.6.32-504.1.3.el6.x86_64/build/include/.. SUBDIRS=$PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= modules
make[1]: Entering directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/linux/af_vsock.o
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/linux/notify.o
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/linux/notifyQState.o
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/linux/stats.o
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/linux/util.o
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/linux/vsockAddr.o
  CC [M]  /tmp/modconfig-lea0x8/vsock-only/driverLog.o
  LD [M]  /tmp/modconfig-lea0x8/vsock-only/vsock.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /tmp/modconfig-lea0x8/vsock-only/vsock.mod.o
  LD [M]  /tmp/modconfig-lea0x8/vsock-only/vsock.ko.unsigned
  NO SIGN [M] /tmp/modconfig-lea0x8/vsock-only/vsock.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.32-504.1.3.el6.x86_64'
/usr/bin/make -C $PWD SRCROOT=$PWD/. \
          MODULEBUILDDIR= postbuild
make[1]: Entering directory `/tmp/modconfig-lea0x8/vsock-only'
make[1]: `postbuild' is up to date.
make[1]: Leaving directory `/tmp/modconfig-lea0x8/vsock-only'
cp -f vsock.ko ./../vsock.o
make: Leaving directory `/tmp/modconfig-lea0x8/vsock-only'
Starting VMware services:
   Virtual machine monitor                                 [  OK  ]
   Virtual machine communication interface                 [  OK  ]
   VM communication interface socket family                [  OK  ]
   Blocking file system                                    [  OK  ]
   Virtual ethernet                                        [  OK  ]
   VMware Authentication Daemon                            [  OK  ]
   Shared Memory Available                                 [  OK  ]

VMware Workstation should now work the next time you start it.

My System Configuration

  • VMware Workstation 10.0.4
  • CentOS 6.6 x86 64-bit

References

Increase Buffer Size Within the Windows Command Prompt Window

  1. Open Command Prompt
  2. Click the upper-left corner of the Command Prompt window, and then click Properties.
  3. Click the Options tab.
  4. In Command History, type or select 999 in Buffer Size, and then type or select 5 in Number of Buffers.
  5. Click the Layout tab.
  6. In Screen Buffer Size, type or select 9999 in Height.
  7. In the Apply Properties dialog box, click Save properties for future windows with same title.

References

MySQL Enterprise Audit: “[ERROR] Plugin ‘audit_log’ init function returned error”

Problem

The MySQL Enterprise Audit plugin stops logging to the audit log file /var/log/mysql/audit.log when the MySQL service starts. The following errors may be seen in the MySQL error log file /var/log/mysql/error.log:

 130228  2:39:50 [ERROR] Plugin 'audit_log' init function returned error.
 130228  2:39:50 [ERROR] Plugin 'audit_log' registration as a AUDIT failed.

Solution

When the audit log plugin opens its log file, it checks whether the XML declaration and opening root element tag need to be written and writes them if so. When the audit log plugin terminates, it writes a closing tag to the file.

If the log file exists at open time, the plugin checks whether the file ends with an tag and truncates it if so before writing any elements. If the log file already exists but does not end with or the tag cannot be truncated, the plugin considers the file malformed and fails to initialize. This can occur if the server crashes or is killed with the audit log plugin running. No logging occurs until the problem is rectified.

To deal with this problem, you must either remove or rename the malformed log file:

$ sudo mv /var/log/mysql/audit.log /var/log/mysql/audit.log.`date +%Y%m%d`

Login to the MySQL service as a user with the SUPER privilege. Delete and re-install the audit plugin.

>SELECT * FROM mysql.plugin;
+-----------+--------------+
| name      | dl           |
+-----------+--------------+
| audit_log | audit_log.so |
+-----------+--------------+
1 row in set (0.00 sec)
 
>DELETE FROM mysql.plugin WHERE name='audit_log';
Query OK, 1 row affected (0.01 sec)
 
>SELECT * FROM mysql.plugin;
Empty set (0.00 sec)
 
>INSTALL PLUGIN audit_log SONAME 'audit_log.so';
Query OK, 0 rows affected (0.03 sec)
 
>SHOW PLUGINS;
+--------------------------+----------+--------------------+--------------+-------------+
| Name                     | Status   | Type               | Library      | License     |
+--------------------------+----------+--------------------+--------------+-------------+
| binlog                   | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| mysql_native_password    | ACTIVE   | AUTHENTICATION     | NULL         | PROPRIETARY |
| mysql_old_password       | ACTIVE   | AUTHENTICATION     | NULL         | PROPRIETARY |
| MEMORY                   | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| MRG_MYISAM               | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| CSV                      | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| MyISAM                   | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| BLACKHOLE                | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| FEDERATED                | DISABLED | STORAGE ENGINE     | NULL         | PROPRIETARY |
| PERFORMANCE_SCHEMA       | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| InnoDB                   | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| INNODB_TRX               | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_LOCKS             | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_LOCK_WAITS        | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_CMP               | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_CMP_RESET         | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_CMPMEM            | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_CMPMEM_RESET      | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_BUFFER_PAGE       | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_BUFFER_PAGE_LRU   | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| INNODB_BUFFER_POOL_STATS | ACTIVE   | INFORMATION SCHEMA | NULL         | PROPRIETARY |
| ARCHIVE                  | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| partition                | ACTIVE   | STORAGE ENGINE     | NULL         | PROPRIETARY |
| audit_log                | ACTIVE   | AUDIT              | audit_log.so | PROPRIETARY |
+--------------------------+----------+--------------------+--------------+-------------+
24 rows in set (0.00 sec)
 
>SELECT * FROM mysql.plugin;
+-----------+--------------+
| name      | dl           |
+-----------+--------------+
| audit_log | audit_log.so |
+-----------+--------------+
1 row in set (0.00 sec)

Verify that the audit log file /var/log/mysql/audit.log was recreated and that new MySQL connections are being logged to it.

If the INSTALL PLUGIN statement executed above fails with the output:

>INSTALL PLUGIN audit_log SONAME 'audit_log.so';
ERROR 1123 (HY000): Can't initialize function 'audit_log'; Plugin initialization function failed.

it may be because you did not move the malformed audit log file out of the way as stated above. Try:

$ sudo mv /var/log/mysql/audit.log /tmp

Finally, install the plug-in again:

>INSTALL PLUGIN audit_log SONAME 'audit_log.so';
Query OK, 0 rows affected (0.03 sec)

Hopefully, it will complete successfully this time.

My System Configuration

  • MySQL Enterprise Server 5.5.35

References

Apache Directory Studio “LDAP: error code 13 – confidentiality required for update”

Problem

I am able to use the LDAP client Apache Directory Studio to connect to and browse my OpenLDAP server. However, when I attempt to make a change, I get the error:

Error while executing LDIF
 - [LDAP: error code 13 - confidentiality required for update]
  java.lang.Exception: [LDAP: error code 13 - confidentiality required for update]
	at org.apache.directory.studio.connection.core.io.api.DirectoryApiConnectionWrapper.checkResponse(DirectoryApiConnectionWrapper.java:1280)
	at org.apache.directory.studio.connection.core.io.api.DirectoryApiConnectionWrapper.access$600(DirectoryApiConnectionWrapper.java:109)
	at org.apache.directory.studio.connection.core.io.api.DirectoryApiConnectionWrapper$4.run(DirectoryApiConnectionWrapper.java:726)
	at org.apache.directory.studio.connection.core.io.api.DirectoryApiConnectionWrapper.runAndMonitor(DirectoryApiConnectionWrapper.java:1175)
	at org.apache.directory.studio.connection.core.io.api.DirectoryApiConnectionWrapper.checkConnectionAndRunAndMonitor(DirectoryApiConnectionWrapper.java:1109)
	at org.apache.directory.studio.connection.core.io.api.DirectoryApiConnectionWrapper.modifyEntry(DirectoryApiConnectionWrapper.java:748)
	at org.apache.directory.studio.ldapbrowser.core.jobs.ImportLdifRunnable.importLdifRecord(ImportLdifRunnable.java:514)
	at org.apache.directory.studio.ldapbrowser.core.jobs.ImportLdifRunnable.importLdif(ImportLdifRunnable.java:272)
	at org.apache.directory.studio.ldapbrowser.core.jobs.ExecuteLdifRunnable.executeLdif(ExecuteLdifRunnable.java:157)
	at org.apache.directory.studio.ldapbrowser.core.jobs.ExecuteLdifRunnable.run(ExecuteLdifRunnable.java:123)
	at org.apache.directory.studio.ldapbrowser.core.jobs.UpdateEntryRunnable.run(UpdateEntryRunnable.java:59)
	at org.apache.directory.studio.connection.ui.RunnableContextRunner$1.run(RunnableContextRunner.java:112)
	at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121)
 
  [LDAP: error code 13 - confidentiality required for update]

Note that “confidentiality” means a TLS secured connection.

Solution

I resolved this problem by changing the Provider setting for this connection from “Apache Directory LDAP Client API” to “JNDI (Java Naming and Directory Interface)”. However, I am not entirely certain as to why this resolves the problem.

2014-01-18_apache-directory-studio-error

My System Configuration

  • Client OS: Linux Mint 16 Petra x86 64-bit
  • Apache Directory Studio Version: 2.0.0.v20130628
  • OpenJDK Runtime Environment 1.7.0_25
  • LDAP Server: OpenLDAP 2.4.21
  • LDAP Server OS: Ubuntu Lucid 10.04 LTS x86 64-bit

References

Easily Configure a Host-Based Firewall on Ubuntu to Block Incoming Connections

The default firewall configuration tool for Ubuntu is UFW (uncomplicated firewall). It was developed to ease iptables firewall configuration. By default UFW is disabled, and there are no packet filter rules in the Linux kernel:

# iptables -L -n --line-numbers
Chain INPUT (policy ACCEPT)
num  target     prot opt source               destination         
 
Chain FORWARD (policy ACCEPT)
num  target     prot opt source               destination         
 
Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination

When you turn UFW on, it uses a default set of rules that should be fine for the average home user. In short, all incoming connections will be denied, thus protecting the system from intruders. To turn UFW on:

# ufw enable
Firewall is active and enabled on system startup

Once enabled, you are done! All future incoming connections will be denied. This configuration will be reloaded at boot.

You can easily view the status of ufw:

# ufw status
Status: active

If you are interested in seeing what UFW did, then run the following command to output the current UFW rules that are applied to your iptables. While it looks like UFW has done a lot, most of this is benign. UFW basically sets up a framework in order for it to easily add additional rules in the future, as well as faciliting logging.

# iptables -L -n --line-numbers
Chain INPUT (policy DROP)
num  target     prot opt source               destination         
1    ufw-before-logging-input  all  --  0.0.0.0/0            0.0.0.0/0           
2    ufw-before-input  all  --  0.0.0.0/0            0.0.0.0/0           
3    ufw-after-input  all  --  0.0.0.0/0            0.0.0.0/0           
4    ufw-after-logging-input  all  --  0.0.0.0/0            0.0.0.0/0           
5    ufw-reject-input  all  --  0.0.0.0/0            0.0.0.0/0           
6    ufw-track-input  all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain FORWARD (policy DROP)
num  target     prot opt source               destination         
1    ufw-before-logging-forward  all  --  0.0.0.0/0            0.0.0.0/0           
2    ufw-before-forward  all  --  0.0.0.0/0            0.0.0.0/0           
3    ufw-after-forward  all  --  0.0.0.0/0            0.0.0.0/0           
4    ufw-after-logging-forward  all  --  0.0.0.0/0            0.0.0.0/0           
5    ufw-reject-forward  all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain OUTPUT (policy ACCEPT)
num  target     prot opt source               destination         
1    ufw-before-logging-output  all  --  0.0.0.0/0            0.0.0.0/0           
2    ufw-before-output  all  --  0.0.0.0/0            0.0.0.0/0           
3    ufw-after-output  all  --  0.0.0.0/0            0.0.0.0/0           
4    ufw-after-logging-output  all  --  0.0.0.0/0            0.0.0.0/0           
5    ufw-reject-output  all  --  0.0.0.0/0            0.0.0.0/0           
6    ufw-track-output  all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-after-forward (1 references)
num  target     prot opt source               destination         
 
Chain ufw-after-input (1 references)
num  target     prot opt source               destination         
1    ufw-skip-to-policy-input  udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:137
2    ufw-skip-to-policy-input  udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:138
3    ufw-skip-to-policy-input  tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:139
4    ufw-skip-to-policy-input  tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:445
5    ufw-skip-to-policy-input  udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:67
6    ufw-skip-to-policy-input  udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:68
7    ufw-skip-to-policy-input  all  --  0.0.0.0/0            0.0.0.0/0            ADDRTYPE match dst-type BROADCAST
 
Chain ufw-after-logging-forward (1 references)
num  target     prot opt source               destination         
1    LOG        all  --  0.0.0.0/0            0.0.0.0/0            limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW BLOCK] "
 
Chain ufw-after-logging-input (1 references)
num  target     prot opt source               destination         
1    LOG        all  --  0.0.0.0/0            0.0.0.0/0            limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW BLOCK] "
 
Chain ufw-after-logging-output (1 references)
num  target     prot opt source               destination         
 
Chain ufw-after-output (1 references)
num  target     prot opt source               destination         
 
Chain ufw-before-forward (1 references)
num  target     prot opt source               destination         
1    ufw-user-forward  all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-before-input (1 references)
num  target     prot opt source               destination         
1    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
2    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
3    ufw-logging-deny  all  --  0.0.0.0/0            0.0.0.0/0            state INVALID
4    DROP       all  --  0.0.0.0/0            0.0.0.0/0            state INVALID
5    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0            icmptype 3
6    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0            icmptype 4
7    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0            icmptype 11
8    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0            icmptype 12
9    ACCEPT     icmp --  0.0.0.0/0            0.0.0.0/0            icmptype 8
10   ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            udp spt:67 dpt:68
11   ufw-not-local  all  --  0.0.0.0/0            0.0.0.0/0           
12   ACCEPT     udp  --  0.0.0.0/0            224.0.0.251          udp dpt:5353
13   ACCEPT     udp  --  0.0.0.0/0            239.255.255.250      udp dpt:1900
14   ufw-user-input  all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-before-logging-forward (1 references)
num  target     prot opt source               destination         
 
Chain ufw-before-logging-input (1 references)
num  target     prot opt source               destination         
 
Chain ufw-before-logging-output (1 references)
num  target     prot opt source               destination         
 
Chain ufw-before-output (1 references)
num  target     prot opt source               destination         
1    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
2    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
3    ufw-user-output  all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-logging-allow (0 references)
num  target     prot opt source               destination         
1    LOG        all  --  0.0.0.0/0            0.0.0.0/0            limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW ALLOW] "
 
Chain ufw-logging-deny (2 references)
num  target     prot opt source               destination         
1    RETURN     all  --  0.0.0.0/0            0.0.0.0/0            state INVALID limit: avg 3/min burst 10
2    LOG        all  --  0.0.0.0/0            0.0.0.0/0            limit: avg 3/min burst 10 LOG flags 0 level 4 prefix "[UFW BLOCK] "
 
Chain ufw-not-local (1 references)
num  target     prot opt source               destination         
1    RETURN     all  --  0.0.0.0/0            0.0.0.0/0            ADDRTYPE match dst-type LOCAL
2    RETURN     all  --  0.0.0.0/0            0.0.0.0/0            ADDRTYPE match dst-type MULTICAST
3    RETURN     all  --  0.0.0.0/0            0.0.0.0/0            ADDRTYPE match dst-type BROADCAST
4    ufw-logging-deny  all  --  0.0.0.0/0            0.0.0.0/0            limit: avg 3/min burst 10
5    DROP       all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-reject-forward (1 references)
num  target     prot opt source               destination         
 
Chain ufw-reject-input (1 references)
num  target     prot opt source               destination         
 
Chain ufw-reject-output (1 references)
num  target     prot opt source               destination         
 
Chain ufw-skip-to-policy-forward (0 references)
num  target     prot opt source               destination         
1    DROP       all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-skip-to-policy-input (7 references)
num  target     prot opt source               destination         
1    DROP       all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-skip-to-policy-output (0 references)
num  target     prot opt source               destination         
1    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-track-input (1 references)
num  target     prot opt source               destination         
 
Chain ufw-track-output (1 references)
num  target     prot opt source               destination         
1    ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            state NEW
2    ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            state NEW
 
Chain ufw-user-forward (1 references)
num  target     prot opt source               destination         
 
Chain ufw-user-input (1 references)
num  target     prot opt source               destination         
 
Chain ufw-user-limit (0 references)
num  target     prot opt source               destination         
1    LOG        all  --  0.0.0.0/0            0.0.0.0/0            limit: avg 3/min burst 5 LOG flags 0 level 4 prefix "[UFW LIMIT BLOCK] "
2    REJECT     all  --  0.0.0.0/0            0.0.0.0/0            reject-with icmp-port-unreachable
 
Chain ufw-user-limit-accept (0 references)
num  target     prot opt source               destination         
1    ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0           
 
Chain ufw-user-logging-forward (0 references)
num  target     prot opt source               destination         
 
Chain ufw-user-logging-input (0 references)
num  target     prot opt source               destination         
 
Chain ufw-user-logging-output (0 references)
num  target     prot opt source               destination         
 
Chain ufw-user-output (1 references)
num  target     prot opt source               destination

This is the rule in the INPUT chain above that drops incoming connections:

DROP       all  --  0.0.0.0/0            0.0.0.0/0

You may want to install gufw. It is a graphical user interface for UFW that provides an easy and intuitive way to manage your Linux firewall. It supports common tasks such as allowing or blocking ports. There is a status switch that can be turned on and off, which basically performs the commands “ufw enable” and “ufw disable“.

2014-01-14_gufw

My System Configuration

  • Linux Mint 16 Petra x86 64-bit

References

Configure Ubuntu to be Verbose at Boot

Configure Ubuntu to output more verbosely to the screen at boot.

GRUB 2

Configure GRUB 2 /etc/default/grub:

# How long to time out showing blank screen. Commenting this out or setting no value 
# after the = sign means the menu will be displayed for the number of seconds 
# designated by GRUB_TIMEOUT. 
#GRUB_HIDDEN_TIMEOUT=
# Setting to false means grub menu will be displayed
GRUB_HIDDEN_TIMEOUT_QUIET=false
# How many seconds the grub menu will be displayed 
# before defaulting the value set in GRUB_DEFAULT
GRUB_TIMEOUT=5
# Remove the kernel parameters "quiet" and "splash"
GRUB_CMDLINE_LINUX_DEFAULT=""
# Disable graphical terminal
GRUB_TERMINAL=console

After updating, run

update-grub

to create a new /boot/grub/grub.cfg file.

My System Configuration

  • Linux Mint 16 Petra x86 64-bit

References

Configure CentOS 6 to be Verbose at Boot

Configure CentOS 6 to output more verbosely to the screen at boot.

GRUB

Have GRUB display the menu interface. GRUB will still automatically boot the default entry, unless interrupted.
Modify the GRUB configuration file /boot/grub/grub.conf. Comment out the line that contains “hiddenmenu”.

#hiddenmenu

Linux Kernel

Modify the GRUB configuration file /boot/grub/grub.conf. Remove the kernel parameters “quite” and “rhgb” from each kernel entry.

“quiet” causes the kernel to not print out messages while the kernel loads.

“rhgb” enables the Red Hat graphical boot after the kernel loads. You may see this as a logo being displayed to the screen and a progress bar.

Before:

#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
#hiddenmenu
title CentOS (2.6.32-431.3.1.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-431.3.1.el6.x86_64 ro root=/dev/mapper/system-root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=system/root rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=system/swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
        initrd /initramfs-2.6.32-431.3.1.el6.x86_64.img
title CentOS (2.6.32-431.1.2.0.1.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-431.1.2.0.1.el6.x86_64 ro root=/dev/mapper/system-root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=system/root rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=system/swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
        initrd /initramfs-2.6.32-431.1.2.0.1.el6.x86_64.img
title CentOS (2.6.32-431.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=/dev/mapper/system-root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=system/root rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=system/swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
        initrd /initramfs-2.6.32-431.el6.x86_64.img

After:

#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
#hiddenmenu
title CentOS (2.6.32-431.3.1.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-431.3.1.el6.x86_64 ro root=/dev/mapper/system-root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=system/root rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=system/swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-431.3.1.el6.x86_64.img
title CentOS (2.6.32-431.1.2.0.1.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-431.1.2.0.1.el6.x86_64 ro root=/dev/mapper/system-root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=system/root rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=system/swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-431.1.2.0.1.el6.x86_64.img
title CentOS (2.6.32-431.el6.x86_64)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=/dev/mapper/system-root rd_NO_LUKS LANG=en_US.UTF-8 rd_LVM_LV=system/root rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=system/swap  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-431.el6.x86_64.img

This is all you need to do. Unlike Ubuntu, you do not need to run a script such as update-grub. Future kernel package updates will not add the “rhgb” and “quiet” kernel parameters back.

My System Configuration

  • CentOS 6.5 x86 64-bit

References

Running Aide on CentOS 6 Results in Modified mtime and ctime on Directories

Each time aide is run with either the –check or –update option, it always detects differences between the database and the filesystem. Specifically, the mtime and ctime on certain directories:

# aide --check
 
AIDE found differences between database and filesystem!!
Start timestamp: 2014-01-05 08:03:47
 
Summary:
  Total number of files:        39240
  Added files:                  0
  Removed files:                0
  Changed files:                20
 
---------------------------------------------------
Changed files:
---------------------------------------------------
 
changed: /usr/sbin
changed: /usr/libexec
changed: /usr/libexec/gcc/x86_64-redhat-linux/4.4.4
changed: /usr/libexec/getconf
changed: /usr/libexec/polkit-1
changed: /usr/libexec/utempter
changed: /usr/libexec/awk
changed: /usr/bin
changed: /usr/lib64
changed: /usr/lib64/pm-utils/bin
changed: /usr/lib64/nss/unsupported-tools
changed: /usr/lib64/sa
changed: /usr/lib64/perl5/CORE
changed: /root
changed: /root/.viminfo
changed: /lib/udev
changed: /bin
changed: /lib64
changed: /lib64/dbus-1
changed: /sbin
 
--------------------------------------------------
Detailed information about changes:
---------------------------------------------------
 
Directory: /usr/sbin
  Mtime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:20
  Ctime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:20
 
Directory: /usr/libexec
  Mtime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:21
  Ctime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:21
 
Directory: /usr/libexec/gcc/x86_64-redhat-linux/4.4.4
  Mtime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:21
  Ctime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:21
 
Directory: /usr/libexec/getconf
  Mtime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:21
  Ctime    : 2014-01-05 08:00:49              , 2014-01-05 08:01:21
 
Directory: /usr/libexec/polkit-1
  Mtime    : 2014-01-05 08:00:50              , 2014-01-05 08:01:21
  Ctime    : 2014-01-05 08:00:50              , 2014-01-05 08:01:21
 
Directory: /usr/libexec/utempter
  Mtime    : 2014-01-05 08:00:50              , 2014-01-05 08:01:21
  Ctime    : 2014-01-05 08:00:50              , 2014-01-05 08:01:21
 
Directory: /usr/libexec/awk
  Mtime    : 2014-01-05 08:00:50              , 2014-01-05 08:01:21
  Ctime    : 2014-01-05 08:00:50              , 2014-01-05 08:01:21
 
Directory: /usr/bin
  Mtime    : 2014-01-05 08:00:57              , 2014-01-05 08:01:29
  Ctime    : 2014-01-05 08:00:57              , 2014-01-05 08:01:29
 
Directory: /usr/lib64
  Mtime    : 2014-01-05 08:01:09              , 2014-01-05 08:01:42
  Ctime    : 2014-01-05 08:01:09              , 2014-01-05 08:01:42
 
Directory: /usr/lib64/pm-utils/bin
  Mtime    : 2014-01-05 08:01:09              , 2014-01-05 08:01:42
  Ctime    : 2014-01-05 08:01:09              , 2014-01-05 08:01:42
 
Directory: /usr/lib64/nss/unsupported-tools
  Mtime    : 2014-01-05 08:01:09              , 2014-01-05 08:01:42
  Ctime    : 2014-01-05 08:01:09              , 2014-01-05 08:01:42
 
Directory: /usr/lib64/sa
  Mtime    : 2014-01-05 08:01:10              , 2014-01-05 08:01:43
  Ctime    : 2014-01-05 08:01:10              , 2014-01-05 08:01:43
 
Directory: /usr/lib64/perl5/CORE
  Mtime    : 2014-01-05 08:01:10              , 2014-01-05 08:01:44
  Ctime    : 2014-01-05 08:01:10              , 2014-01-05 08:01:44
 
Directory: /root
  Mtime    : 2014-01-05 07:59:25              , 2014-01-05 08:03:45
  Ctime    : 2014-01-05 07:59:25              , 2014-01-05 08:03:45
 
File: /root/.viminfo
  Inode    : 267392                           , 267393
 
Directory: /lib/udev
  Mtime    : 2014-01-05 08:01:14              , 2014-01-05 08:01:48
  Ctime    : 2014-01-05 08:01:14              , 2014-01-05 08:01:48
 
Directory: /bin
  Mtime    : 2014-01-05 08:01:15              , 2014-01-05 08:01:49
  Ctime    : 2014-01-05 08:01:15              , 2014-01-05 08:01:49
 
Directory: /lib64
  Mtime    : 2014-01-05 08:01:16              , 2014-01-05 08:01:50
  Ctime    : 2014-01-05 08:01:16              , 2014-01-05 08:01:50
 
Directory: /lib64/dbus-1
  Mtime    : 2014-01-05 08:01:16              , 2014-01-05 08:01:50
  Ctime    : 2014-01-05 08:01:16              , 2014-01-05 08:01:50
 
Directory: /sbin
  Mtime    : 2014-01-05 08:01:18              , 2014-01-05 08:01:52
  Ctime    : 2014-01-05 08:01:18              , 2014-01-05 08:01:52

After each execution of aide, the mtime and ctime on these directories are changed. Hence, aide detects and reports these changes.

This is due to prelinking. If you disable prelinking, then this problem will go away. To disable prelinking, modify the configuration file /etc/sysconfig/prelink. Change “PRELINKING=yes” to “PRELINKING=no“. Then manually run /etc/cron.daily/prelink as root. After updating the aide database, subsequent aide checks will not have this problem.

My System Configuration

  • CentOS 6.5 x86 64-bit
  • Aide 0.14
# aide --version
Aide 0.14
 
Compiled with the following options:
 
WITH_MMAP
WITH_POSIX_ACL
WITH_SELINUX
WITH_PRELINK
WITH_XATTR
WITH_LSTAT64
WITH_READDIR64
WITH_ZLIB
WITH_GCRYPT
WITH_AUDIT
CONFIG_FILE = "/etc/aide.conf"

References

Two-Step Authentication for SSH on CentOS 6 Using Google Authenticator

Google Authenticator implements TOTP (timebased one-time-password) security tokens from RFC6238 via the Google mobile app Google Authenticator. The Authenticator provides a six digit one-time password users must provide in addition to their username and password to login, sometimes branded “two-step authentication”. Here, we install and configure a pluggable authentication module (PAM) which allows login using one-time passcodes.

Download and Install

At the time of this writing, only an old version of libpam-google-authenticator is available in the EPEL package repository. Hence, we are going to compile it from source. First, install prerequisites:

# yum install make gcc pam-devel

TOTP (timebased one-time-password) security tokens are time sensitive. Hence, make sure that your system has ntpd running, and is configured to start the service at boot:

# service ntpd start
Starting ntpd:                                             [  OK  ]
# chkconfig  ntpd on

Then download and install libpam-google-authenticator from source:

# cd /tmp
# wget http://google-authenticator.googlecode.com/files/libpam-google-authenticator-1.0-source.tar.bz2
# bunzip2 libpam-google-authenticator-1.0-source.tar.bz2
# tar xf libpam-google-authenticator-1.0-source.tar
# cd libpam-google-authenticator-1.0
# make
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o google-authenticator.o google-authenticator.c
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o base32.o base32.c
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o hmac.o hmac.c
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o sha1.o sha1.c
gcc -g   -o google-authenticator google-authenticator.o base32.o hmac.o sha1.o  -ldl
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o pam_google_authenticator.o pam_google_authenticator.c
gcc -shared -g   -o pam_google_authenticator.so pam_google_authenticator.o base32.o hmac.o sha1.o -lpam
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o demo.o demo.c
gcc -DDEMO --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o pam_google_authenticator_demo.o pam_google_authenticator.c
gcc -g   -rdynamic -o demo demo.o pam_google_authenticator_demo.o base32.o hmac.o sha1.o  -ldl
gcc -DTESTING --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden        \
              -o pam_google_authenticator_testing.o pam_google_authenticator.c
gcc -shared -g   -o pam_google_authenticator_testing.so pam_google_authenticator_testing.o base32.o hmac.o sha1.o -lpam
gcc --std=gnu99 -Wall -O2 -g -fPIC -c  -fvisibility=hidden  -o pam_google_authenticator_unittest.o pam_google_authenticator_unittest.c
gcc -g   -rdynamic -o pam_google_authenticator_unittest pam_google_authenticator_unittest.o base32.o hmac.o sha1.o -lc  -ldl
 
# make install
cp pam_google_authenticator.so /lib64/security
cp google-authenticator /usr/local/bin

Set Up Google Authenticator

Before configuring SSH, first set up Google Authenticator. Run “google-authenticator” as the user you wish to log in with via SSH. You will be prompted with a few questions.

Do you want me to update your "~/.google_authenticator" file (y/n) y
 
https://www.google.com/chart?chs=200x200&chld=M|0&cht=qr&chl=otpauth://totp/user@server%3Fsecret%3DABCD12E3FGHIJKLMN
Your new secret key is: ABCD12E3FGHIJKLMN
Your verification code is 98765432
Your emergency scratch codes are:
  01234567
  89012345
  67890123
  45678901
  23456789
 
Do you want to disallow multiple uses of the same authentication
token? This restricts you to one login about every 30s, but it increases
your chances to notice or even prevent man-in-the-middle attacks (y/n) y
 
By default, tokens are good for 30 seconds and in order to compensate for
possible time-skew between the client and the server, we allow an extra
token before and after the current time. If you experience problems with poor
time synchronization, you can increase the window from its default
size of 1:30min to about 4min. Do you want to do so (y/n) y
 
If the computer that you are logging into isn't hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting (y/n) y

These settings are stored in the user’s ~/.google_authenticator file.

Copy and paste the URL into your browser and scan the QR code that is displayed with the app Google Authenticator on your mobile device. If you can’t scan the QR code, then you can enter the information manually with the given secret key and verification code. A new verification code should be displayed every 30 seconds.

Emergency one-time use verification codes are also given for you to write down in a secure place in case you were to not have your mobile device with you.

Configure PAM

Have PAM require Google Authenticator for SSH authentication. Modify /etc/pam.d/sshd and add the line “auth required pam_google_authenticator.so” at the top.

#%PAM-1.0
auth       required     pam_google_authenticator.so
auth       required     pam_sepermit.so
auth       include      password-auth
account    required     pam_nologin.so
account    include      password-auth
password   include      password-auth
# pam_selinux.so close should be the first session rule
session    required     pam_selinux.so close
session    required     pam_loginuid.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session    required     pam_selinux.so open env_params
session    optional     pam_keyinit.so force revoke
session    include      password-auth

This will require all users to use Google Authenticator for SSH authentication. To only require those users with Google Authenticator configured for their account (the ~/.google_authenticator file exists), then instead enter “auth required pam_google_authenticator.so nullok“.

The order in which you place items in this file matters. Given this configuration, you will first be prompted for your Google Authenticator verification code, then for your system account password when you SSH into the system.

Configure the SSH Service

Modify /etc/ssh/sshd_config. Verify these settings:

PasswordAuthentication yes
ChallengeResponseAuthentication yes
UsePAM yes

Restart the SSH service:

# service sshd restart

When you SSH into the system as a user configured for Google Authenticator, you will have to enter the verification code that is displayed in you Google Authenticator app, and then by your system password at the next prompt:

login as: root
Verification code: 01234567
Password: *******
#

If you have any problems, look in the /var/log/secure system log file.

If you have SELinux enabled, you may not be able to login, and get this error in /var/log/secure:

Jan  3 23:42:50 hostname sshd(pam_google_authenticator)[1654]: Failed to update secret file "/home/username/.google_authenticator"
Jan  3 23:42:50 hostname  sshd[1652]: error: PAM: Cannot make/remove an entry for the specified session for username from 192.168.0.5

This is probably due /home/username/.google_authenticator not having an appropriate Type Enforcement (TE):

# ls -Z /home/username/.google_authenticator
-r--------. username username unconfined_u:object_r:user_home_t:s0 /home/username/.google_authenticator

See here for additional information on this issue.

Skip Google Authenticator Authentication if Logging in from the Local Network

You may trust systems on you local network enough not not require that SSH connections from them use Google Authenticator. If so, modify /etc/pam.d/sshd so that it looks like this:

auth [success=1 default=ignore] pam_access.so accessfile=/etc/security/access-local.conf
auth       required     pam_google_authenticator.so

Then add the file /etc/security/access-local.conf with the contents:

# Google Authenticator can be skipped on local network
+ : ALL : 192.168.0.0/24
+ : ALL : LOCAL
- : ALL : ALL

This assumes your local network is subnet 192.168.0.0/24.

My System Configuration

  • CentOS 6.5 x86 64-bit
  • Google Authenticator libpam 1.0

References

Prevent Brute-Force SSH Attacks Using iptables

Prevent (or at least slow down) a brute-force SSH attack.

By default, iptables on a CentOS 6 SSH server allows all inbound SSH traffic on port 22. See /etc/sysconfig/iptables:

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT

Modify /etc/sysconfig/iptables to the following in order to allow a particular IP to initiate 5 new SSH connections within a window of 60s. If additional new SSH connections are opened for that IP, then all packets from that IP will be dropped, and the incident will be logged to /var/log/messages. After 60s that IP will be able to open 5 new SSH connections, and so on. Please note that when I say that a new SSH connection is made that I do not mean to imply the SSH authentication was successful. Just that the two hosts initiated a new TCP/IP connection over port 22.

*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set --name SSH -j ACCEPT
-A INPUT -p tcp --dport 22 -m recent --update --seconds 60 --hitcount 5 --rttl --name SSH -j LOG --log-prefix "BRUTE_FORCE_SSH"
-A INPUT -p tcp --dport 22 -m recent --update --seconds 60 --hitcount 5 --rttl --name SSH -j DROP
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
# service iptables stop && service iptables start

My System Configuration

  • CentOS 6.5 x86 64-bit

References

David Lehman's System Administration Blog