HON95-wiki/config/general/linux-examples.md

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title: Linux Examples breadcrumbs:

• title: Configuration
• title: General --- {% include header.md %}

Commands

General Monitoring

• For more specific monitoring, see the other sections.
• htop:
  • ncurses-based process viewer like top, but prettier and more interactive.
  • Install (APT): apt install htop
  • Usage: htop (interactive)
• glances:
  • Homepage: Glances
  • Install (PyPI for latest version): pip3 install glances
  • ncurses-based viewer for e.g. basic system info, top-like process info, network traffic and disk traffic.
  • Usage: glances (interactive)
• dstat:
  • A versatile replacement for vmstat, iostat and ifstat (according to itself).
  • Prints scrolling output for showing a lot of types of general metrics, one line of columns for each time step.
  • Usage: dstat <options> [interval] [count]
    • Default interval is 1s, default count is unlimited.
    • The values shown are the average since the last interval ended.
    • For intervals over 1s, the last row will update itself each second until the delay has been reached and a new line is created. The values shown are averages since the last final value (when the last line was finalized), so e.g. a 10s interval gives a final line showing a 10s average.
    • The first line is always a snapshot, i.e. all rate-based metrics are 0 or some absolute value.
    • If any column options are provided, they will replace the default ones and are displayed in the order specified.
  • Special options:
    • -C <>: Comma-separated list of CPUs/cores to show for, including total.
    • -D <>: Same but for disks.
    • -N <>: Same but for NICs.
    • -f: Show stats for all devices (not aggregated).
  • Useful metrics:
    • -t: Current time.
    • -p: Process stats (by runnable, uninterruptible, new) (changes per second).
    • -y: Total interrupt and context switching stats (by interrupts, context switches) (events per second).
    • -l: Load average stats (1 min, 5 mins, 15 mins) (total system load multiplied by number of cores).
    • -c: CPU stats (by system, user, idle, wait) (percentage of total).
    • --cpu-use: Per-CPU usage (by CPU) (percentage).
    • -m: Memory stats (by used, buffers, cache, free) (bytes).
    • -g: Paging stats (by in, out) (count per second).
    • -s: Swap stats (by used, free) (total).
    • -r: Storage request stats (by read, write) (requests per second).
    • -d: Storage throughput stats (by read, write) (bytes per second).
    • -n: Network throughput stats (by recv, send) (bytes per second).
    • --socket: Network socket stats (by total, tcp, udp, raw, ip-fragments)
  • Useful plugins (metrics):
    • --net-packets: Network request stats (by recv, send) (packets per second).
  • Examples:
    • General overview (CPU, RAM, ints/csws, disk, net): dstat -tcmyrdn --net-packets 60
    • Network overview (CPU, ints/csws, net): dstat -tcyn --net-packets 60
    • Process overview (CPU, RAM, ints/csws, paging, process, sockets): dstat -tcmygp --socket 60

File Systems and Logical Volume Managers

• Partition disk: gdisk <dev> or fdisk <dev>
• Create filesystem: mkfs.<fs> <dev>
• Modify fstab:
  • Test it with mount -a to make sure it doesn't have errors that may cause boot to fail.
  • Run systemctl daemon-reload to avoid having systemd remount stuff that was removed from fstab or other weird shit.
• Benchmark with IOzone:
  • Install (Debian): apt install iozone3
  • It uses the current dir.
  • Test with various record sizes and file sizes: iozone -a
  • Benchmark: iozone -t1 (1 thread)
  • Plot results: TODO It should be doable with gnuplot somehow.

Files

• Search:
  • By UID: find / -user <UID>
  • Without a user: find / -nouser
  • With setuid permission bit: find / -perm /4000
  • Recursive search and replace: find <dir> \( -type d -name .git -prune \) -o -type f -print0 | xargs -0 sed -i 's/123/456/g'
    • -type d -name .git -prune skips .git directories and can be excluded outside of git repos.
• Usage:
  • du -sh <dirs>
  • K4DirStat (GUI) (package k4dirstat)
• Shred files:
  • shred --remove --zero <file>

Fun

• Color text from STDIN: lolcat
• cowsay
• fortune

Hardware

• Show hardware: lshw
  • Run as root for more info.
  • Specify -X to show GUI (requires lshw-gtk).
• Show hardware topology: lstopo (requires hwloc)
  • lstopo will try to present as a GUI. Use lstopo-no-graphics to force console output.
• Show PCI devices: lspci
• Show block devices: lsblk
• Show USB devices: lsusb
• Show CPUs: lscpu

Installations and Packages

APT (Debian)

• Find packages depending on the package: apt rdepends --installed <package>
• Quickly add new repo: add-apt-repository <repo-line
  • It will add the line to /etc/apt/sources.list, where you can manually remove it again.
• Keys:
  • List: apt-key list
    • It will also show which file contains it.
  • Remvoe key: apt-key del <key-id>
    • The 8-digit hex key ID may either be found on pub line or as the last 8 hex digits on the continuation line.

Network

• Monitor usage:
  • nload <if>
  • iftop -i <if>
  • speedometer -t <if> -r <if> [...]
  • dstat -tcyn --net-packets 60
• Monitor per-process usage:
  • nethog
• Test throughput:
  • Internet: speedtest (from speedtest.net)
  • Internal: iperf3
• Show interfaces and addresses (with ip):
  • General: ip [-c] [-46] [-s] {l[ink]|a[ddress]} [-br] [sh [if]]
  • Option -c: Color.
  • Option {-4|-6}: IPv4 or IPv6 only.
  • Option -s: Show stats (bytes, packets, errors, dropped, etc. for RX and TX).
  • Option -br: One line per interface (MAC address and status for link, addresses for address).
  • Argument scope global: Only global addresses (excludes localhost/host, link-local/link, etc.).
• Show neighbors (with ip):
  • General: ip [-c] [-46] n[eighbor]
  • Option -c: Color.
  • Option {-4|-6}: IPv4 or IPv6 only.
• Show routes (with ip):
  • General: ip [-c] [-46] r[oute]
  • Option -c: Color.
  • Option {-4|-6}: IPv4 or IPv6 only.
• Show multicast addresses (with ip):
  • General: ip [-c] [-46] ma[ddress]
  • Option -c: Color.
  • Option {-4|-6}: IPv4 or IPv6 only.
• Show multicast routes (with ip):
  • General: ip [-c] [-46] mr[oute]
  • Option -c: Color.
  • Option {-4|-6}: IPv4 or IPv6 only.
• Show sockets (with ss):
  • Example: ss -tulpn
  • Note: ss replaces netstat and is mostly option compatible.
  • Option tu: Include TCP and UDP sockets (no UNIX sockets).
  • Option l: Include listening sockets (no client sockets).
  • Option p: Show protocol (requires root).
  • Option n: Don't translate port numbers to common service names.
• Show misc. stats:
  • Show kernel SNMP counters: nstat
  • Show per-protocol stats: netstat -s
• Bring interface up or down:
  • Note: Your network manager probably has a more appropriate way to do this.
  • Directly up or down interface: ip link set dev <if> {up|down}
• Traffic shaping and link simulation:
  • See tc to simulate e.g. random packet drop, random latencies, limited bandwidth etc.

Tcpdump

• Typical usage: tcpdump -i <interface> -nn -v [filter]
• Options:
  • -w <>.pcap: Write to capture file instead of formatted to STDOUT.
  • -i <if>: Interface to listen on. Defaults to a random-ish interface.
  • -nn: Don't resolve hostnames or ports.
  • -s<n>: How much of the packets to capture. Use 0 for unlimited (full packet).
  • -v/-vv: Details to show about packets. More V's for more details.
  • -l: Line buffered more, for better stability when piping to e.g. grep.
• Filters:
  • Can consist of complex logical statements using parenthesis, not/!, and/&& and or/||. Make sure to quote the filter to avoid interference from the shell.
  • Protocol: ip, ip6, icmp, icmp6, tcp, udp, ``
  • Ports: port <n>
  • IP address: host <addr>, dst <addr>, src <addr>
  • IPv6 router solicitations and advertisements: icmp6 and (ip6[40] = 133 or ip6[40] = 134) (133 for RS and 134 for RA)
  • IPv6 neighbor solicitations and advertisements: icmp6 and (ip6[40] = 135 or ip6[40] = 136) (135 for NS and 136 for NA)
  • DHCPv4: ip and udp and (port 67 and port 68)
  • DHCPv6: ip6 and udp and (port 547 and port 546)

Memory

• NUMA stats:
  • numastat (from package numactl)

Performance and Power Efficiency

• Set the CPU frequency scaling governor mode:
  • High performance: echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
  • Power save: echo powersave | ...
• Show current core frequencies: grep "cpu MHz" /proc/cpuinfo | cut -d' ' -f3

Profiling

• time (timing commands):
  • Provided both as a shell built-in time and as /usr/bin/time, use the latter.
  • Typical usage: /usr/bin/time -p <command>
  • Options:
    • -p for POSIX output (one line per time)
    • -v for interesting system info about the process.
  • It give the wall time, time spent in usermode and time spent in kernel mode.
• strace (trace system calls and signals):
  • In standard mode, it runs the full command and traces/prints all syscalls (including arguments and return value).
  • Syntax: strace [options] <command>
  • Useful options:
    • -c: Show summary/overview only. (Hints at which syscalls are worth looking more into.)
    • -f: Trace forked child processes too.
    • -e trace=<syscalls>: Only trace the specified comma-separated list of syscalls.

Security

• Show CPU vulnerabilities: tail -n +1 /sys/devices/system/cpu/vulnerabilities/*

Storage

• Test read speed: hdparm -t <dev> (safe)
• Show IO load for devices: iostat [-dxpm] [-t] [interval]
  • -d: Show only device usage.
  • -x and -p: Include extended attributes and partitions.
  • -t and interval: Show timestamp and repeat every x seconds.
• Show IO usage for processes: iotop -o [-a]

System

• Version info:
  • Release info files:
    • Debian (and Ubuntu): /etc/debian_version
    • RHEL: /etc/redhat-release
    • CentOS: /etc/centos-release
  • General release info: uname -a
  • Slightly more distro-specific release info: lsb_release -a
• Monitor system load:
  • uptime
  • iostat [-c] [-t] [interval]
• Monitor processes:
  • ps (e.g. ps aux or ps ax o uid,user:12,pid,comm)
• Monitor a mix of things: See the "general monitoring" section.
• Monitor interrupts:
  • irqtop
  • watch -n0.1 /proc/interrupts
• Stress test with stress-ng:
  • Install (Debian): apt install stress-ng
  • Stress CPU: stress-ng -c $(nproc) -t 600

Tasks

Burn Windows ISO

1. Install the graphical application woeusb from ppa:nilarimogard/webupd8.

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