What You’ll Learn
- How to use Linux commands to view the file system, system statistics, and file configurations
- How to use Linux commands to view the system performance
- How to verify connections on the Linux system
What You’ll Need
- A Linux server with Python installed
- A client computer to use Secure Shell (SSH) to the Linux server if the server is remote
Linux is an open-source operating system that is used by many devices today, including computers, consumer appliances, and mobile, networking, and IoT devices. The best part of all is that Linux is free. This has contributed to the success of Linux as well as its continued evolution.
The Linux ls command is used to list the names and features of files and directories.
[root@linux /]$ ls
afs bin boot dev etc home lib lib64 media mnt opt proc root run sbin srv sys tmp usr var
However, using the ls without its many options will only display generic information.
If you want to list all hidden files and folders, use the -a option, but if you wish to display the permission of the files and folders, then the -l option will also be needed.
[root@linux /]$ ls -la
total 24
dr-xr-xr-x. 18 root root 235 Nov 5 2022 .
dr-xr-xr-x. 18 root root 235 Nov 5 2022 ..
dr-xr-xr-x. 2 root root 6 Aug 9 2022 afs
lrwxrwxrwx. 1 root root 7 Aug 9 2022 bin -> usr/bin
dr-xr-xr-x. 7 root root 4096 Aug 19 19:07 boot
drwxr-xr-x. 18 root root 3780 Aug 20 15:13 dev
drwxr-xr-x. 115 root root 8192 Aug 20 02:08 etc
drwxr-xr-x. 3 root root 19 Oct 24 2022 home
lrwxrwxrwx. 1 root root 7 Aug 9 2022 lib -> usr/lib
lrwxrwxrwx. 1 root root 9 Aug 9 2022 lib64 -> usr/lib64
drwxr-xr-x. 2 root root 6 Aug 9 2022 media
drwxr-xr-x. 2 root root 6 Aug 9 2022 mnt
drwxr-xr-x. 2 root root 6 Aug 9 2022 opt
dr-xr-xr-x. 240 root root 0 Dec 31 1969 proc
dr-xr-x---. 2 root root 4096 Aug 20 13:56 root
drwxr-xr-x. 43 root root 1200 Aug 19 21:51 run
lrwxrwxrwx. 1 root root 8 Aug 9 2022 sbin -> usr/sbin
drwxr-xr-x. 2 root root 6 Aug 9 2022 srv
dr-xr-xr-x. 12 root root 0 Mar 31 00:00 sys
drwxrwxrwt. 9 root root 180 Aug 21 12:35 tmp
drwxr-xr-x. 12 root root 144 Nov 5 2022 usr
drwxr-xr-x. 21 root root 4096 Aug 19 19:12 var
Once you display the files and folders on the Linux system using the ls command, you will need the cd command to change directories, allowing you to go into a folder to access the contents.
[root@linux /]$ cd etc/
[root@linux /]$ ls -la
total 1336
drwxr-xr-x. 115 root root 8192 Aug 20 02:08 .
dr-xr-xr-x. 18 root root 235 Nov 5 2022 ..
drwxr-xr-x. 3 root root 101 Jun 30 08:21 abrt
-rw-r--r--. 1 root root 18 Oct 24 2022 adjtime
-rw-r--r--. 1 root root 1529 Jul 20 2022 aliases
drwxr-xr-x. 2 root root 4096 May 4 11:25 alternatives
drwxr-xr-x. 4 root root 58 Nov 5 2022 anaconda
-rw-r--r--. 1 root root 541 Jul 20 2022 anacrontab
-rw-r--r--. 1 root root 1 Jul 20 2022 at.deny
drwxr-x---. 4 root root 100 Apr 27 14:40 audit
drwxr-xr-x. 3 root root 4096 Aug 19 19:05 authselect
-rw-r--r--. 1 root root 15843 Mar 28 23:17 autofs.conf
-rw-------. 1 root root 232 Mar 28 23:17 autofs_ldap_auth.conf
-rw-r--r--. 1 root root 1289 Mar 28 23:17 auto.master
drwxr-xr-x. 2 root root 6 Mar 28 23:17 auto.master.d
-rw-r--r--. 1 root root 519 Mar 28 23:17 auto.misc
-rwxr-xr-x. 1 root root 901 Mar 28 23:17 auto.net
-rwxr-xr-x. 1 root root 2087 Mar 28 23:17 auto.smb
drwxr-xr-x. 2 root root 75 Aug 19 19:04 bash_completion.d
-rw-r--r--. 1 root root 2638 Jul 20 2022 bashrc
-rw-r--r--. 1 root root 535 Apr 21 21:52 bindresvport.blacklist
drwxr-xr-x. 2 root root 6 Mar 31 13:24 binfmt.d
drwxr-xr-x. 2 root root 23 Aug 19 18:57 bluetooth
drwxr-xr-x. 2 root root 29 Dec 1 2022 certmonger
-rw-r--r--. 1 root root 1371 Aug 29 2022 chrony.conf
-rw-r-----. 1 root chrony 540 Aug 29 2022 chrony.keys
drwxr-xr-x. 2 root root 26 Jun 26 07:07 cifs-utils
drwxr-xr-x. 4 root root 42 Jul 12 04:48 cockpit
drwxr-xr-x. 7 root root 134 Aug 19 18:58 containers
drwxr-xr-x. 2 root root 21 Nov 5 2022 cron.d
drwxr-xr-x. 2 root root 6 Jul 20 2022 cron.daily
-rw-r--r--. 1 root root 0 Jul 20 2022 cron.deny
drwxr-xr-x. 2 root root 22 Nov 5 2022 cron.hourly
drwxr-xr-x. 2 root root 6 Jul 20 2022 cron.monthly
-rw-r--r--. 1 root root 451 Jul 20 2022 crontab
drwxr-xr-x. 2 root root 6 Jul 20 2022 cron.weekly
drwxr-xr-x. 6 root root 81 Nov 5 2022 crypto-policies
-rw-------. 1 root root 0 Nov 5 2022 crypttab
-rw-r--r--. 1 root root 1401 Jul 20 2022 csh.cshrc
-rw-r--r--. 1 root root 1087 Jul 20 2022 csh.login
drwxr-xr-x. 4 root root 78 Jun 6 16:59 dbus-1
drwxr-xr-x. 4 root root 31 Nov 5 2022 dconf
drwxr-xr-x. 2 root root 27 Nov 5 2022 debuginfod
drwxr-xr-x. 2 root root 33 Nov 5 2022 default
drwxr-xr-x. 2 root root 6 Jul 21 2022 depmod.d
drwxr-x---. 3 root root 61 Aug 20 13:49 dhcp
-rw-r--r--. 1 root root 5169 May 4 17:53 DIR_COLORS
-rw-r--r--. 1 root root 5251 May 4 17:53 DIR_COLORS.lightbgcolor
drwxr-xr-x. 8 root root 128 Jul 28 08:42 dnf
-rw-r--r--. 1 root root 28485 Apr 3 11:01 dnsmasq.conf
drwxr-xr-x. 2 root root 6 Apr 3 11:01 dnsmasq.d
-rw-r--r--. 1 root root 117 Apr 27 07:55 dracut.conf
drwxr-xr-x. 2 root root 6 Apr 27 07:55 dracut.conf.d
-rw-r--r--. 1 root root 0 Jul 23 2022 environment
-rw-r--r--. 1 root root 1362 Jul 20 2022 ethertypes
-rw-r--r--. 1 root root 0 Jul 20 2022 exports
drwxr-xr-x. 2 root root 6 Apr 20 09:25 exports.d
lrwxrwxrwx. 1 root root 56 Jul 20 2022 favicon.png -> /usr/share/icons/hicolor/16x16/apps/fedora-logo-icon.png
lrwxrwxrwx. 1 root root 25 Feb 23 10:23 fedora-release -> ../usr/lib/fedora-release
-rw-r--r--. 1 root root 66 Jul 20 2022 filesystems
drwxr-x---. 8 root root 4096 Aug 19 19:53 firewalld
drwxr-xr-x. 3 root root 20 Nov 5 2022 fonts
-rw-r--r--. 1 root root 20 Feb 24 2022 fprintd.conf
-rw-r--r--. 1 root root 590 Nov 5 2022 fstab
-rw-r--r--. 1 root root 38 Jul 20 2022 fuse.conf
drwxr-xr-x. 4 root root 110 Aug 19 19:04 fwupd
drwxr-xr-x. 2 root root 6 Jul 21 2022 gcrypt
-rw-r--r--. 1 root root 265 Jun 30 22:06 gdbinit
drwxr-xr-x. 2 root root 6 Jun 30 22:06 gdbinit.d
drwxr-xr-x. 2 root root 6 Oct 18 2022 gnupg
-rw-r--r--. 1 root root 94 Jul 21 2022 GREP_COLORS
drwxr-xr-x. 4 root root 40 Nov 5 2022 groff
-rw-r--r--. 1 root root 756 Aug 19 19:51 group
-rw-r--r--. 1 root root 743 Aug 19 19:12 group-
lrwxrwxrwx. 1 root root 22 Apr 10 13:05 grub2.cfg -> ../boot/grub2/grub.cfg
lrwxrwxrwx. 1 root root 22 Apr 10 13:05 grub2-efi.cfg -> ../boot/grub2/grub.cfg
drwx------. 2 root root 4096 Aug 19 19:04 grub.d
----------. 1 root root 616 Aug 19 19:51 gshadow
----------. 1 root root 606 Aug 19 19:12 gshadow-
drwxr-xr-x. 3 root root 20 Nov 16 2022 gss
drwxr-xr-x. 2 root root 87 Nov 5 2022 gssproxy
-rw-r--r--. 1 root root 9 Jul 20 2022 host.conf
-rw-r--r--. 1 root root 11 Aug 19 20:33 hostname
-rw-r--r--. 1 root root 386 Jul 20 2022 hosts
-rw-r--r--. 1 root root 5799 Apr 20 09:25 idmapd.conf
drwxr-xr-x. 3 root root 20 Nov 5 2022 initial-setup
-rw-r--r--. 1 root root 490 Mar 31 13:24 inittab
-rw-r--r--. 1 root root 943 Jul 20 2022 inputrc
drwxr-xr-x. 3 root root 19 Nov 27 2022 ipa
drwxr-xr-x. 2 root root 159 Nov 5 2022 iproute2
drwxr-xr-x. 2 root root 25 Nov 5 2022 iscsi
lrwxrwxrwx. 1 root root 16 Feb 23 10:23 issue -> ../usr/lib/issue
drwxr-xr-x. 2 root root 27 Feb 23 10:23 issue.d
lrwxrwxrwx. 1 root root 20 Feb 23 10:23 issue.net -> ../usr/lib/issue.net
drwxr-xr-x. 4 root root 33 Nov 5 2022 kdump
-rw-r--r--. 1 root root 8892 Nov 5 2022 kdump.conf
drwxr-xr-x. 3 root root 38 Mar 31 13:24 kernel
-rw-r--r--. 1 root root 880 Nov 16 2022 krb5.conf
drwxr-xr-x. 2 root root 106 Nov 16 2022 krb5.conf.d
-rw-r--r--. 1 root root 23163 Aug 19 19:51 ld.so.cache
-rw-r--r--. 1 root root 28 Jan 10 2023 ld.so.conf
drwxr-xr-x. 2 root root 6 Jan 11 2023 ld.so.conf.d
-rw-r-----. 1 root root 191 Apr 27 13:26 libaudit.conf
drwxr-xr-x. 3 root root 20 Nov 5 2022 libblockdev
drwxr-xr-x. 2 root root 4096 Nov 5 2022 libibverbs.d
drwxr-xr-x. 2 root root 35 Nov 5 2022 libnl
drwxr-xr-x. 6 root root 4096 Aug 19 18:57 libreport
drwxr-xr-x. 2 root root 62 May 15 06:28 libssh
-rw-r--r--. 1 root root 2393 Sep 23 2022 libuser.conf
-rw-r--r--. 1 root root 19 Oct 24 2022 locale.conf
lrwxrwxrwx. 1 root root 32 Oct 24 2022 localtime -> ../usr/share/zoneinfo/US/Eastern
-rw-r--r--. 1 root root 8676 Mar 27 08:13 login.defs
-rw-r--r--. 1 root root 493 Apr 16 2021 logrotate.conf
drwxr-xr-x. 2 root root 4096 Aug 19 19:12 logrotate.d
drwxr-xr-x. 6 root root 100 Nov 5 2022 lvm
-rw-r--r--. 1 root root 33 Oct 24 2022 machine-id
-rw-r--r--. 1 root root 111 Jul 26 2022 magic
-rw-r--r--. 1 root root 272 Apr 27 2021 mailcap
-rw-r--r--. 1 root root 5122 Aug 3 2022 makedumpfile.conf.sample
-rw-r--r--. 1 root root 5235 Jul 21 2022 man_db.conf
-rw-r--r--. 1 root root 69857 Apr 27 2021 mime.types
-rw-r--r--. 1 root root 782 Jul 20 2022 mke2fs.conf
drwxr-xr-x. 2 root root 54 Aug 19 19:04 modprobe.d
drwxr-xr-x. 2 root root 6 Mar 31 13:24 modules-load.d
-rw-r--r--. 1 root root 0 Jul 20 2022 motd
drwxr-xr-x. 2 root root 21 Nov 5 2022 motd.d
lrwxrwxrwx. 1 root root 19 Aug 4 2022 mtab -> ../proc/self/mounts
drwxr-xr-x. 2 root root 6 Nov 15 2022 multipath
drwxr-x---. 2 root named 6 Jul 20 06:17 named
-rw-r-----. 1 root named 1934 Aug 19 20:48 named.conf
-rw-r-----. 1 root named 12288 Aug 19 19:13 .named.conf.swp
-rw-r-----. 1 root named 1034 Jul 20 06:17 named.rfc1912.zones
-rw-r--r--. 1 root named 686 Jul 20 06:17 named.root.key
-rw-r--r--. 1 root root 767 Apr 21 21:52 netconfig
drwxr-xr-x. 7 root root 134 Apr 20 07:38 NetworkManager
-rw-r--r--. 1 root root 58 Jul 20 2022 networks
-rw-r--r--. 1 root root 1468 Apr 20 09:25 nfs.conf
-rw-r--r--. 1 root root 3604 Apr 20 09:25 nfsmount.conf
drwx------. 3 root root 66 Nov 5 2022 nftables
lrwxrwxrwx. 1 root root 29 Aug 19 19:05 nsswitch.conf -> /etc/authselect/nsswitch.conf
drwxr-xr-x. 2 root root 6 Dec 9 2022 oddjob
-rw-r--r--. 1 root root 4922 Dec 9 2022 oddjobd.conf
drwxr-xr-x. 2 root root 70 Dec 9 2022 oddjobd.conf.d
drwxr-xr-x. 2 root root 75 Nov 5 2022 openhpi
drwxr-xr-x. 4 root root 50 Mar 7 18:52 openldap
lrwxrwxrwx. 1 root root 16 Aug 8 09:10 opensc-aarch64.conf -> /etc/opensc.conf
-rw-r--r--. 1 root root 441 Aug 8 09:08 opensc.conf
drwxr-xr-x. 2 root root 6 Aug 9 2022 opt
lrwxrwxrwx. 1 root root 21 Feb 23 10:23 os-release -> ../usr/lib/os-release
drwxr-xr-x. 3 root root 23 Nov 23 2022 ostree
drwxr-xr-x. 2 root root 48 Jan 24 2023 PackageKit
drwxr-xr-x. 2 root root 4096 Aug 19 19:05 pam.d
-rw-r--r--. 1 root root 1767 Aug 19 19:51 passwd
-rw-r--r--. 1 root root 1723 Aug 19 19:12 passwd-
-rw-r--r--. 1 root root 263 Jun 23 06:36 passwdqc.conf
-rw-r--r--. 1 root root 2872 Jul 22 2022 pinforc
drwxr-xr-x. 3 root root 21 Jul 24 03:39 pkcs11
drwxr-xr-x. 3 root root 27 Nov 5 2022 pkgconfig
drwxr-xr-x. 10 root root 123 Nov 5 2022 pki
drwxr-xr-x. 2 root root 28 Nov 5 2022 plymouth
drwxr-xr-x. 5 root root 52 Nov 5 2022 pm
drwxr-xr-x. 5 root root 72 Apr 11 06:30 polkit-1
drwxr-xr-x. 2 root root 6 Sep 16 2022 popt.d
-rw-r--r--. 1 root root 233 Jul 20 2022 printcap
-rw-r--r--. 1 root root 1945 Jul 20 2022 profile
drwxr-xr-x. 2 root root 4096 Aug 19 19:04 profile.d
-rw-r--r--. 1 root root 6568 Jul 20 2022 protocols
-rw-------. 1 root root 0 Nov 5 2022 .pwd.lock
drwxr-xr-x. 3 root root 50 Aug 19 19:04 qemu-ga
drwxr-xr-x. 3 root root 20 Mar 31 13:24 rc.d
drwxr-xr-x. 2 root root 25 Sep 19 2022 reader.conf.d
lrwxrwxrwx. 1 root root 14 Feb 23 10:23 redhat-release -> fedora-release
-rw-r--r--. 1 root root 1787 Jul 21 2022 request-key.conf
drwxr-xr-x. 2 root root 77 Nov 5 2022 request-key.d
lrwxrwxrwx. 1 root root 39 Nov 5 2022 resolv.conf -> ../run/systemd/resolve/stub-resolv.conf
-rw-r-----. 1 root named 100 Aug 19 19:21 rndc.key
-rw-r--r--. 1 root root 1634 Jan 10 2023 rpc
drwxr-xr-x. 2 root root 6 Apr 24 08:06 rpm
-rw-r--r--. 1 root root 458 Oct 21 2022 rsyncd.conf
-rw-r--r--. 1 root root 3223 Jul 27 2022 rsyslog.conf
drwxr-xr-x. 2 root root 6 Jul 27 2022 rsyslog.d
drwxr-xr-x. 2 root root 64 Aug 19 19:12 rwtab.d
drwxr-xr-x. 2 root root 61 Aug 19 18:57 samba
drwxr-xr-x. 2 root root 6 Aug 18 2022 sasl2
drwxr-xr-x. 7 root root 4096 Feb 1 2023 security
drwxr-xr-x. 3 root root 79 Mar 27 08:07 selinux
-rw-r--r--. 1 root root 10593 Jul 21 2022 sensors3.conf
drwxr-xr-x. 2 root root 6 Jul 21 2022 sensors.d
-rw-r--r--. 1 root root 701745 Jul 20 2022 services
-rw-r--r--. 1 root root 216 Feb 27 13:23 sestatus.conf
drwxr-xr-x. 2 root root 33 Feb 27 11:38 setroubleshoot
----------. 1 root root 984 Aug 19 19:51 shadow
----------. 1 root root 963 Aug 19 19:12 shadow-
-rw-r--r--. 1 root root 44 Jul 20 2022 shells
drwxr-xr-x. 2 root root 62 Nov 5 2022 skel
drwxr-xr-x. 3 root root 74 Aug 19 19:04 smartmontools
drwxr-xr-x. 6 root root 86 Nov 5 2022 sos
drwxr-xr-x. 4 root root 4096 Jul 21 11:31 ssh
drwxr-xr-x. 2 root root 91 Aug 19 18:55 ssl
drwx------. 4 root root 31 Jun 26 07:07 sssd
drwxr-xr-x. 2 root root 6 Aug 9 2022 statetab.d
-rw-r--r--. 1 root root 19 Oct 24 2022 subgid
-rw-r--r--. 1 root root 0 Jul 20 2022 subgid-
-rw-r--r--. 1 root root 19 Oct 24 2022 subuid
-rw-r--r--. 1 root root 0 Jul 20 2022 subuid-
-rw-r-----. 1 root root 4316 Mar 1 12:08 sudo.conf
-r--r-----. 1 root root 4375 Mar 1 12:04 sudoers
drwxr-x---. 2 root root 6 Mar 1 12:08 sudoers.d
drwxr-xr-x. 3 root root 24 Feb 23 10:23 swid
drwxr-xr-x. 3 root root 4096 Aug 19 19:51 sysconfig
-rw-r--r--. 1 root root 449 Mar 31 13:24 sysctl.conf
drwxr-xr-x. 2 root root 28 Mar 31 13:24 sysctl.d
drwxr-xr-x. 5 root root 4096 Mar 31 13:24 systemd
lrwxrwxrwx. 1 root root 14 Feb 23 10:23 system-release -> fedora-release
lrwxrwxrwx. 1 root root 29 Feb 23 10:23 system-release-cpe -> ../usr/lib/system-release-cpe
drwxr-xr-x. 2 root root 6 Jun 6 04:41 terminfo
drwxr-xr-x. 2 root root 6 Mar 31 13:24 tmpfiles.d
drwxr-xr-x. 3 root root 51 Aug 19 18:56 tpm2-tss
-rw-r--r--. 1 root root 375 Jul 20 06:17 trusted-key.key
drwxr-xr-x. 4 root root 68 Aug 19 19:08 udev
drwxr-xr-x. 3 root root 82 Nov 5 2022 udisks2
-rw-r--r--. 1 root root 208 Nov 5 2022 .updated
-rw-r--r--. 1 root root 616 Dec 27 2022 updatedb.conf
-rw-r--r--. 1 root root 28 Oct 24 2022 vconsole.conf
-rw-r--r--. 1 root root 4017 Jul 21 03:09 vimrc
-rw-r--r--. 1 root root 1183 Jul 21 03:09 virc
drwxr-xr-x. 4 root root 4096 Aug 19 19:04 vmware-tools
-rw-r--r--. 1 root root 4925 Jul 23 2022 wgetrc
-rw-r--r--. 1 root root 380 Jan 3 2022 whois.conf
drwxr-xr-x. 2 root root 33 Nov 5 2022 wpa_supplicant
drwxr-xr-x. 6 root root 70 Nov 5 2022 X11
-rw-r--r--. 1 root root 817 Jul 20 2022 xattr.conf
drwxr-xr-x. 4 root root 38 Nov 5 2022 xdg
drwxr-xr-x. 2 root root 4096 Jan 29 2023 yum.repos.d
[root@linux etc]$
Notice that the Linux prompt information changes from [root@linux /] to [root@linux etc]$, reflecting the directory that you are in. The pwd command can also be used to display the present working directory.
[root@linux /]$ pwd
/etc
The Linux more command is a command-line utility that allows users to view text files one page at a time.
For example, let’s assume that you are in the /etc directory, and you want to view the content of a file called hosts. The more command can be used to display the content of that file.
[root@linux /]$ more hosts
# Loopback entries; do not change.
# For historical reasons, localhost precedes localhost.localdomain:
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
# See hosts(5) for proper format and other examples:
# 192.168.1.10 foo.mydomain.org foo
# 192.168.1.13 bar.mydomain.org bar
(END)
Notice that the more command puts you into a view mode, meaning that you can view more pages by using the space bar on your computer. Once you reach the end of the document, you will see (END) at the bottom. In order to exit, you will need to type the letter q to exit the view mode.
The Linux top command allows the user to see which resources are taking up the most CPU on the system based on system process and application names. It gives you an overall view of the current state of the CPU utilization. Once the top command is used, it will put you into a top-view mode that will display the information in real time.
top - 13:49:52 up 1 day, 17:39, 1 user, load average: 0.09, 0.08, 0.08
Tasks: 178 total, 1 running, 177 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.2 us, 0.2 sy, 0.0 ni, 99.4 id, 0.0 wa, 0.1 hi, 0.1 si, 0.0 st
MiB Mem : 7824.7 total, 6236.1 free, 536.1 used, 1052.6 buff/cache
MiB Swap: 7824.0 total, 7824.0 free, 0.0 used. 7039.0 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
716 systemd+ 20 0 17688 6656 5888 S 0.7 0.1 7:45.83 systemd-oomd
19142 spawn 20 0 225248 3200 2560 R 0.7 0.0 0:00.11 top
9692 named 20 0 641304 32232 7680 S 0.3 0.4 7:03.56 named
1 root 20 0 174536 15800 9384 S 0.0 0.2 0:16.74 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.50 kthreadd
3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp
4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par_gp
5 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 slub_flushwq
6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 netns
11 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_percpu_wq
13 root 20 0 0 0 0 I 0.0 0.0 0:00.00 rcu_tasks_kthread
14 root 20 0 0 0 0 I 0.0 0.0 0:00.00 rcu_tasks_rude_kthread
15 root 20 0 0 0 0 I 0.0 0.0 0:00.00 rcu_tasks_trace_kthread
16 root 20 0 0 0 0 S 0.0 0.0 0:00.38 ksoftirqd/0
17 root 20 0 0 0 0 I 0.0 0.0 0:27.38 rcu_preempt
18 root rt 0 0 0 0 S 0.0 0.0 0:00.33 migration/0
19 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/0
There are a lot of values being displayed using the top command, including:
us: Amount of time the CPU spends executing processes for people in "user space."
sy: Amount of time spent running system "kernel space" processes.
ni: Amount of time spent executing processes with a manually set nice value.
id: Amount of CPU idle time.
wa: Amount of time the CPU spends waiting for I/O to complete.
hi: Amount of time spent servicing hardware interrupts.
si: Amount of time spent servicing software interrupts.
st: Amount of time lost due to running virtual machines ("steal time").
The column headings information displays the following:
PID: Process ID.
USER: The owner of the process.
PR: Process priority.
NI: The nice value of the process.
VIRT: Amount of virtual memory used by the process.
RES: Amount of resident memory used by the process.
SHR: Amount of shared memory used by the process.
S: Status of the process. (See the list below for the values this field can take).
%CPU: The share of CPU time used by the process since the last update.
%MEM: The share of physical memory used.
TIME+: Total CPU time used by the task in hundredths of a second.
COMMAND: The command name or command line (name + options).
Because the top command will display information in real time, it will show the status information as follows:
D: Uninterruptible sleep
R: Running
S: Sleeping
T: Traced (stopped)
Z: Zombie
To exit from top-view mode, you will need to use the q key on your keyboard.
The Linux netstat command is used to print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. We will be using it to print network connection and routing table information.
To display both listening and nonlistening sockets, you can use the -a option.
[root@linux /]$ netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 localhost:domain 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN
tcp 0 0 dns-master:domain 0.0.0.0:* LISTEN
tcp 0 0 localhost:domain 0.0.0.0:* LISTEN
tcp 0 0 localhost:domain 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:hostmon 0.0.0.0:* LISTEN
tcp 0 0 localhost:rndc 0.0.0.0:* LISTEN
tcp 0 172 dns-master:ssh 172.16.1.36:56450 ESTABLISHED
tcp6 0 0 [::]:websm [::]:* LISTEN
tcp6 0 0 [::]:ssh [::]:* LISTEN
tcp6 0 0 [::]:hostmon [::]:* LISTEN
udp 0 0 0.0.0.0:hostmon 0.0.0.0:*
udp 0 0 dns-master:domain 0.0.0.0:*
udp 0 0 dns-master:domain 0.0.0.0:*
udp 0 0 dns-master:domain 0.0.0.0:*
udp 0 0 dns-master:domain 0.0.0.0:*
udp 0 0 localhost:domain 0.0.0.0:*
udp 0 0 localhost:domain 0.0.0.0:*
udp 0 0 localhost:domain 0.0.0.0:*
udp 0 0 localhost:domain 0.0.0.0:*
udp 0 0 localhost:domain 0.0.0.0:*
udp 0 0 localhost:domain 0.0.0.0:*
udp 0 0 0.0.0.0:bootps 0.0.0.0:*
udp 0 0 localhost:323 0.0.0.0:*
udp6 0 0 [::]:hostmon [::]:*
udp6 0 0 localhost:323 [::]:*
udp6 0 0 dns-maste:dhcpv6-client [::]:*
raw 0 0 0.0.0.0:icmp 0.0.0.0:* 7
raw6 0 0 [::]:ipv6-icmp [::]:* 7
Notice that it will display the hostname information under the Local Address. To display the IP address instead, you will need to use the -n option.
[root@linux /]$ netstat -an
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 127.0.0.54:53 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp 0 0 192.168.1.26:53 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:5355 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:953 0.0.0.0:* LISTEN
tcp 0 172 192.168.1.26:22 172.16.1.36:56450 ESTABLISHED
tcp6 0 0 :::9090 :::* LISTEN
tcp6 0 0 :::22 :::* LISTEN
tcp6 0 0 :::5355 :::* LISTEN
udp 0 0 0.0.0.0:5355 0.0.0.0:*
udp 0 0 192.168.1.26:53 0.0.0.0:*
udp 0 0 192.168.1.26:53 0.0.0.0:*
udp 0 0 192.168.1.26:53 0.0.0.0:*
udp 0 0 192.168.1.26:53 0.0.0.0:*
udp 0 0 127.0.0.1:53 0.0.0.0:*
udp 0 0 127.0.0.1:53 0.0.0.0:*
udp 0 0 127.0.0.1:53 0.0.0.0:*
udp 0 0 127.0.0.1:53 0.0.0.0:*
udp 0 0 127.0.0.54:53 0.0.0.0:*
udp 0 0 127.0.0.53:53 0.0.0.0:*
udp 0 0 0.0.0.0:67 0.0.0.0:*
udp 0 0 127.0.0.1:323 0.0.0.0:*
udp6 0 0 :::5355 :::*
udp6 0 0 ::1:323 :::*
udp6 0 0 fe80::a1bf:3dd6:350:546 :::*
raw 0 0 0.0.0.0:1 0.0.0.0:*
raw6 0 0 :::58 :::*
In order to display all ports that are listening on the Linux server, you can use the grep filter.
[root@linux /]$ netstat -an | grep LISTEN
tcp 0 0 127.0.0.54:53 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp 0 0 192.168.1.26:53 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:5355 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:953 0.0.0.0:* LISTEN
tcp6 0 0 :::9090 :::* LISTEN
tcp6 0 0 :::22 :::* LISTEN
tcp6 0 0 :::5355 :::* LISTEN
The grep | LISTEN filter is very useful because it allows the administrator to see which services are being advertised on the server and which IP/port is being used to make it accessible to the user.
If you use the grep | ESTABLISHED filter, it will allow the administrator to see who is connected to the server using a certain IP/port.
[root@linux /]$ netstat -an | grep ESTABLISHED
tcp 0 0 192.168.1.26:22 172.16.1.36:56450 ESTABLISHED
udp 0 0 192.168.1.26:56495 198.97.190.53:53 ESTABLISHED
The -r option allows the administrator of the Linux server to see which routing table information is populated.
[root@linux /]$ netstat -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
default _gateway 0.0.0.0 UG 0 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
If the administrator wants to see multicast information on all interfaces, they can use the -g option instead.
[root@linux /]$ netstat -g
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 224.0.0.1
eth0 1 224.0.0.252
eth0 1 224.0.0.1
wlan0 1 224.0.0.1
lo 1 ff02::1
lo 1 ff01::1
eth0 1 ff02::1:ff69:467
eth0 1 ff02::1:3
eth0 1 ff02::1:ff02:c715
eth0 1 ff02::1
eth0 1 ff01::1
wlan0 1 ff02::1
wlan0 1 ff01::1