Chapter 5. Working with containers

Procedure

1. Display the type of operating system of the container based on the registry.access.redhat.com/ubi8/ubi container image using the cat /etc/os-release command:

   $ podman run --rm registry.access.redhat.com/ubi8/ubi cat /etc/os-release
   NAME="Red Hat Enterprise Linux"
   ...
   ID="rhel"
   ...
   HOME_URL="https://www.redhat.com/"
   BUG_REPORT_URL="https://bugzilla.redhat.com/"
   
   REDHAT_BUGZILLA_PRODUCT=" Red Hat Enterprise Linux 8"
   ...

2. Optional: List all containers.

   $ podman ps
   CONTAINER ID  IMAGE   COMMAND  CREATED  STATUS  PORTS   NAMES

   Because of the --rm option you should not see any container. The container was removed.

Procedure

1. Run the container named myubi based on the registry.redhat.io/ubi8/ubi image:

   $ podman run --name=myubi -it registry.access.redhat.com/ubi8/ubi /bin/bash
   [root@6ccffd0f6421 /]#

   • The -i option creates an interactive session. Without the -t option, the shell stays open, but you cannot type anything to the shell.
   • The -t option opens a terminal session. Without the -i option, the shell opens and then exits.

2. Install the procps-ng package containing a set of system utilities (for example ps, top, uptime, and so on):

   [root@6ccffd0f6421 /]# yum install procps-ng

3. Use the ps -ef command to list current processes:

   # ps -ef
   UID          PID    PPID  C STIME TTY          TIME CMD
   root           1       0  0 12:55 pts/0    00:00:00 /bin/bash
   root          31       1  0 13:07 pts/0    00:00:00 ps -ef

4. Enter exit to exit the container and return to the host:

   # exit

5. Optional: List all containers:

   $ podman ps
   CONTAINER ID  IMAGE                               COMMAND    CREATED         STATUS                     PORTS   NAMES
   1984555a2c27  registry.redhat.io/ubi8/ubi:latest  /bin/bash  21 minutes ago  Exited (0) 21 minutes ago          myubi

   You can see that the container is in Exited status.

Procedure

1. Run the container based on registry.redhat.io/rhel8/rsyslog image:

   $ podman run -d registry.redhat.io/rhel8/rsyslog

2. List all containers:

   • To list all running containers:

     $ podman ps
     CONTAINER ID IMAGE              COMMAND         CREATED       STATUS            PORTS NAMES
     74b1da000a11 rhel8/rsyslog /bin/rsyslog.sh 2 minutes ago Up About a minute       musing_brown

   • To list all containers, running or stopped:

     $ podman ps -a
     CONTAINER ID IMAGE         COMMAND    CREATED    STATUS                PORTS NAMES     IS INFRA
     d65aecc325a4 ubi8/ubi      /bin/bash  3 secs ago Exited (0) 5 secs ago peaceful_hopper false
     74b1da000a11 rhel8/rsyslog rsyslog.sh 2 mins ago Up About a minute     musing_brown    false

Procedure

1. Start the myubi container:

   • In the non interactive mode:

     $ podman start myubi

     Alternatively, you can use podman start 1984555a2c27.

   • In the interactive mode, use -a (--attach) and -i (--interactive) options to work with container bash shell:

     $ podman start -a -i myubi

     Alternatively, you can use podman start -a -i 1984555a2c27.

2. Enter exit to exit the container and return to the host:

   [root@6ccffd0f6421 /]# exit

Procedure

1. Run the container named log_test and mount the host /dev/log device inside the container:

   # podman run --name="log_test" -v /dev/log:/dev/log --rm \
     registry.redhat.io/ubi8/ubi logger "Testing logging to the host"

2. Use the journalctl utility to display logs:

   # journalctl -b | grep Testing
   Dec 09 16:55:00 localhost.localdomain root[14634]: Testing logging to the host

   The --rm option removes the container when it exits.

Procedure

1. Run the container named mysyslog:

   # podman run -d --name=mysyslog registry.redhat.io/rhel8/rsyslog

2. Optional: List all containers:

   # podman ps -a
   CONTAINER ID  IMAGE                                    COMMAND          CREATED         STATUS                     PORTS   NAMES
   c56ef6a256f8  registry.redhat.io/rhel8/rsyslog:latest  /bin/rsyslog.sh  20 minutes ago  Up 20 minutes ago                  mysyslog

3. Mount the mysyslog container:

   # podman mount mysyslog
   /var/lib/containers/storage/overlay/990b5c6ddcdeed4bde7b245885ce4544c553d108310e2b797d7be46750894719/merged

4. Display the content of the mount point using ls command:

   # ls /var/lib/containers/storage/overlay/990b5c6ddcdeed4bde7b245885ce4544c553d108310e2b797d7be46750894719/merged
   bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

5. Display the OS version:

   # cat /var/lib/containers/storage/overlay/990b5c6ddcdeed4bde7b245885ce4544c553d108310e2b797d7be46750894719/merged/etc/os-release
   NAME="Red Hat Enterprise Linux"
   VERSION="8 (Ootpa)"
   ID="rhel"
   ID_LIKE="fedora"
   ...

Procedure

1. Set the container network interface to the IP address 10.88.0.44:

   # podman run -d --ip=10.88.0.44 registry.access.redhat.com/rhel8/rsyslog
   efde5f0a8c723f70dd5cb5dc3d5039df3b962fae65575b08662e0d5b5f9fbe85

2. Check that the IP address is set properly:

   # podman inspect efde5f0a8c723 | grep 10.88.0.44
   "IPAddress": "10.88.0.44",

Procedure

1. Execute the rpm -qa command inside the myrsyslog container to list all installed packages:

   $ podman exec -it myrsyslog rpm -qa
   tzdata-2020d-1.el8.noarch
   python3-pip-wheel-9.0.3-18.el8.noarch
   redhat-release-8.3-1.0.el8.x86_64
   filesystem-3.8-3.el8.x86_64
   ...

2. Execute a /bin/bash command in the myrsyslog container:

   $ podman exec -it myrsyslog /bin/bash

3. Install the procps-ng package containing a set of system utilities (for example ps, top, uptime, and so on):

   # yum install procps-ng

4. Inspect the container:

   • To list every process on the system:

     # ps -ef
     UID          PID    PPID  C STIME TTY          TIME CMD
     root           1       0  0 10:23 ?        00:00:01 /usr/sbin/rsyslogd -n
     root           8       0  0 11:07 pts/0    00:00:00 /bin/bash
     root          47       8  0 11:13 pts/0    00:00:00 ps -ef

   • To display file system disk space usage:

     # df -h
     Filesystem      Size  Used Avail Use% Mounted on
     fuse-overlayfs   27G  7.1G   20G  27% /
     tmpfs            64M     0   64M   0% /dev
     tmpfs           269M  936K  268M   1% /etc/hosts
     shm              63M     0   63M   0% /dev/shm
     ...

   • To display system information:

     # uname -r
     4.18.0-240.10.1.el8_3.x86_64

   • To display amount of free and used memory in megabytes:

     # free --mega
     total        used        free      shared  buff/cache   available
     Mem:       2818         615        1183          12         1020        1957
     Swap:      3124           0        3124

Procedure

1. Create a volume:

   $ podman volume create hostvolume

2. Display information about the volume:

   $ podman volume inspect hostvolume
   [
       {
           "name": "hostvolume",
           "labels": {},
           "mountpoint": "/home/username/.local/share/containers/storage/volumes/hostvolume/_data",
           "driver": "local",
           "options": {},
           "scope": "local"
       }
   ]

   Notice that it creates a volume in the volumes directory. You can save the mount point path to the variable for easier manipulation: $ mntPoint=$(podman volume inspect hostvolume --format {{.Mountpoint}}).

   Notice that if you run sudo podman volume create hostvolume, then the mount point changes to /var/lib/containers/storage/volumes/hostvolume/_data.

3. Create a text file inside the directory using the path that is stored in the mntPoint variable:

   $ echo "Hello from host" >> $mntPoint/host.txt

4. List all files in the directory defined by the mntPoint variable:

   $ ls $mntPoint/
   host.txt

5. Run the container named myubi1 and map the directory defined by the hostvolume volume name on the host to the /containervolume1 directory on the container:

   $ podman run -it --name myubi1 -v hostvolume:/containervolume1 registry.access.redhat.com/ubi8/ubi /bin/bash

   Note that if you use the volume path defined by the mntPoint variable (-v $mntPoint:/containervolume1), data can be lost when running podman volume prune command, which removes unused volumes. Always use -v hostvolume_name:/containervolume_name.

6. List the files in the shared volume on the container:

   # ls /containervolume1
   host.txt

   You can see the host.txt file which you created on the host.

7. Create a text file inside the /containervolume1 directory:

   # echo "Hello from container 1" >> /containervolume1/container1.txt

8. Detach from the container with CTRL+p and CTRL+q.

9. List the files in the shared volume on the host, you should see two files:

   $ ls $mntPoint
   container1.rxt  host.txt

   At this point, you are sharing files between the container and host. To share files between two containers, run another container named myubi2.

10. Run the container named myubi2 and map the directory defined by the hostvolume volume name on the host to the /containervolume2 directory on the container:

    $ podman run -it --name myubi2 -v hostvolume:/containervolume2 registry.access.redhat.com/ubi8/ubi /bin/bash

11. List the files in the shared volume on the container:

    # ls /containervolume2
    container1.txt host.txt

    You can see the host.txt file which you created on the host and container1.txt which you created inside the myubi1 container.

12. Create a text file inside the /containervolume2 directory:

    # echo "Hello from container 2" >> /containervolume2/container2.txt

13. Detach from the container with CTRL+p and CTRL+q.

14. List the files in the shared volume on the host, you should see three files:

    $ ls $mntPoint
    container1.rxt  container2.txt host.txt

Procedure

1. Run the myubi container based on the registry.access.redhat.com/ubi8/ubi image:

   $ podman run -dt --name=myubi registry.access.redhat.com/8/ubi

2. Optional: List all containers:

   $ podman ps -a
   CONTAINER ID  IMAGE                                    COMMAND          CREATED     STATUS         PORTS   NAMES
   a6a6d4896142  registry.access.redhat.com/8:latest   /bin/bash        7 seconds ago  Up 7 seconds ago          myubi

3. Attach to the myubi container:

   $ podman attach myubi

4. Create a file named testfile:

   [root@a6a6d4896142 /]# echo "hello" > testfile

5. Detach from the container with CTRL+p and CTRL+q.

6. Export the file system of the myubi as a myubi-container.tar on the local machine:

   $ podman export -o myubi.tar a6a6d4896142

7. Optional: List the current directory content:

   $ ls -l
   -rw-r--r--. 1 user user 210885120 Apr  6 10:50 myubi-container.tar
   ...

8. Optional: Create a myubi-container directory, extract all files from the myubi-container.tar archive. List a content of the myubi-directory in a tree-like format:

   $ mkdir myubi-container
   $ tar -xf myubi-container.tar -C myubi-container
   $ tree -L 1 myubi-container
   ├── bin -> usr/bin
   ├── boot
   ├── dev
   ├── etc
   ├── home
   ├── lib -> usr/lib
   ├── lib64 -> usr/lib64
   ├── lost+found
   ├── media
   ├── mnt
   ├── opt
   ├── proc
   ├── root
   ├── run
   ├── sbin -> usr/sbin
   ├── srv
   ├── sys
   ├── testfile
   ├── tmp
   ├── usr
   └── var
   
   20 directories, 1 file

   You can see that the myubi-container.tar contains the container file system.

9. Import the myubi.tar and saves it as a filesystem image:

   $ podman import myubi.tar myubi-imported
   Getting image source signatures
   Copying blob 277cab30fe96 done
   Copying config c296689a17 done
   Writing manifest to image destination
   Storing signatures
   c296689a17da2f33bf9d16071911636d7ce4d63f329741db679c3f41537e7cbf

10. List all images:

    $ podman images
    REPOSITORY                              TAG     IMAGE ID      CREATED         SIZE
    docker.io/library/myubi-imported       latest  c296689a17da  51 seconds ago  211 MB

11. Display the content of the testfile file:

    $ podman run -it --name=myubi-imported docker.io/library/myubi-imported cat testfile
    hello

Procedure

1. List all containers, running or stopped:

   $ podman ps -a
   CONTAINER ID IMAGE         COMMAND    CREATED    STATUS                PORTS NAMES     IS INFRA
   d65aecc325a4 ubi8/ubi      /bin/bash  3 secs ago Exited (0) 5 secs ago peaceful_hopper false
   74b1da000a11 rhel8/rsyslog rsyslog.sh 2 mins ago Up About a minute     musing_brown    false

2. Remove the containers:

   • To remove the peaceful_hopper container:

     $ podman rm peaceful_hopper

     Notice that the peaceful_hopper container was in Exited status, which means it was stopped and it can be removed immediately.

   • To remove the musing_brown container, first stop the container and then remove it:

     $ podman stop musing_brown
     $ podman rm musing_brown

     NOTE

     • To remove multiple containers:

       $ podman rm clever_yonath furious_shockley

     • To remove all containers from your local system:

       $ podman rm -a