mirror of
https://github.com/linkedin/school-of-sre
synced 2026-01-19 06:58:03 +00:00
102 lines
4.4 KiB
Markdown
102 lines
4.4 KiB
Markdown
##
|
|
|
|
# Command-line tools
|
|
Most of the Linux distributions today come with a set of tools that
|
|
monitor the system's performance. These tools help you measure and
|
|
understand various subsystem statistics (CPU, memory, network, and so
|
|
on). Let's look at some of the tools that are predominantly used.
|
|
|
|
- `ps/top `-- The process status command (ps) displays information
|
|
about all the currently running processes in a Linux system. The
|
|
top command is similar to the ps command, but it periodically
|
|
updates the information displayed until the program is terminated.
|
|
An advanced version of top, called htop, has a more user-friendly
|
|
interface and some additional features. These command-line
|
|
utilities come with options to modify the operation and output of
|
|
the command. Following are some important options supported by the
|
|
ps command.
|
|
|
|
- `-p <pid1, pid2,...>` -- Displays information about processes
|
|
that match the specified process IDs. Similarly, you can use
|
|
`-u <uid>` and `-g <gid>` to display information about
|
|
processes belonging to a specific user or group.
|
|
|
|
- `-a` -- Displays information about other users' processes, as well
|
|
as one's own.
|
|
|
|
- `-x` -- When displaying processes matched by other options,
|
|
includes processes that do not have a controlling terminal.
|
|
|
|
|
|
<p align="center"> Figure 2: Results of top command </p>
|
|
|
|
- `ss` -- The socket statistics command (ss) displays information
|
|
about network sockets on the system. This tool is the successor of
|
|
[netstat](https://man7.org/linux/man-pages/man8/netstat.8.html),
|
|
which is deprecated. Following are some command-line options
|
|
supported by the ss command:
|
|
|
|
- `-t` -- Displays the TCP socket. Similarly, `-u` displays UDP
|
|
sockets, `-x` is for UNIX domain sockets, and so on.
|
|
|
|
- `-l` -- Displays only listening sockets.
|
|
|
|
- `-n` -- Instructs the command to not resolve service names.
|
|
Instead displays the port numbers.
|
|
|
|
 <p align="center"> Figure
|
|
3: List of listening sockets on a system </p>
|
|
|
|
- `free` -- The free command displays memory usage statistics on the
|
|
host like available memory, used memory, and free memory. Most often,
|
|
this command is used with the `-h` command-line option, which
|
|
displays the statistics in a human-readable format.
|
|
|
|
|
|
<p align="center"> Figure 4: Memory statistics on a host in human-readable form </p>
|
|
|
|
- `df --` The df command displays disk space usage statistics. The
|
|
`-i` command-line option is also often used to display
|
|
[inode](https://en.wikipedia.org/wiki/Inode) usage
|
|
statistics. The `-h` command-line option is used for displaying
|
|
statistics in a human-readable format.
|
|
|
|
|
|
<p align="center"> Figure 5:
|
|
Disk usage statistics on a system in human-readable form </p>
|
|
|
|
- `sar` -- The sar utility monitors various subsystems, such as CPU
|
|
and memory, in real time. This data can be stored in a file
|
|
specified with the `-o` option. This tool helps to identify
|
|
anomalies.
|
|
|
|
- `iftop` -- The interface top command (`iftop`) displays bandwidth
|
|
utilization by a host on an interface. This command is often used
|
|
to identify bandwidth usage by active connections. The `-i` option
|
|
specifies which network interface to watch.
|
|
|
|
|
|
<p align="center"> Figure 6: Network bandwidth usage by
|
|
active connection on the host </p>
|
|
|
|
- `tcpdump` -- The tcpdump command is a network monitoring tool that
|
|
captures network packets flowing over the network and displays a
|
|
description of the captured packets. The following options are
|
|
available:
|
|
|
|
- `-i <interface>` -- Interface to listen on
|
|
|
|
- `host <IP/hostname>` -- Filters traffic going to or from the
|
|
specified host
|
|
|
|
- `src/dst` -- Displays one-way traffic from the source (src) or to
|
|
the destination (dst)
|
|
|
|
- `port <port number>` -- Filters traffic to or from a particular
|
|
port
|
|
|
|
|
|
<p align="center"> Figure 7: *tcpdump* of packets on *docker0*
|
|
interface on a host </p> |