Category Archives: Linux

How to check Oracle Exadata Compute node temperature sensors

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On an Exadata compute/database server, check temperature through the server’s ILOM service processor. CellCLI is for storage cells; it is not the compute server’s sensor interface. Oracle: Exadata ambient temperature monitoring

Ambient intake temperature on one node:

ipmitool sunoem cli "show /SYS/T_AMB"

Look for the value in °C and the sensor’s alarm_status.

List temperature sensors:

ipmitool sdr list | grep -iE 'ipmitool sdr list | grep degrees'

Example:

ipmitool sdr list | grep degrees

T_IN_ZONE0 | 40 degrees C | ok
T_IN_ZONE1 | 43 degrees C | ok
T_IN_ZONE2 | 37 degrees C | ok
T_IN_ZONE3 | 43 degrees C | ok
T_OUT_ZONE0 | 41 degrees C | ok
T_OUT_ZONE1 | 44 degrees C | ok
T_OUT_ZONE2 | 43 degrees C | ok
T_OUT_ZONE3 | 47 degrees C | ok
PS0/T_IN | 44 degrees C | ok
PS0/T_OUT | 47 degrees C | ok
PS1/T_IN | 42 degrees C | ok
PS1/T_OUT | 48 degrees C | ok
T_AMB | 31 degrees C | ok

For sensor readings and thresholds, Oracle ILOM also documents ipmitool sensor; available sensors depend on the server model. Oracle ILOM: Display sensor list · Oracle ILOM: IPMItool commands

Check ILOM health and open hardware problems from the ILOM CLI:

show /System health
show /System/Open_Problems
show /SYS/T_AMB

Oracle’s Exadata guidance gives a rack ambient operating range of 5–32 °C, with 21–23 °C as the optimal range. Those are ambient conditions; use each sensor’s reported status and thresholds for component sensors.

Oracle Exadata CellCLI Quick Reference

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Run cellcli on the storage cell, or run a single command from the OS shell with cellcli -e "...". CellCLI commands apply to the local cell; -m starts CellCLI in read-only monitor mode. Oracle: Starting CellCLI · Oracle: CellCLI command syntax

Cell and service health

cellcli -e "list cell detail"
cellcli -e "list cell attributes name,status,cellsrvStatus,msStatus,rsStatus,fanStatus,powerStatus,temperatureStatus"

Check cell status, CELLSRV/MS/RS, and hardware status attributes. list cell detail shows the full set of cell attributes.

Disk health and mapping

cellcli -e "list physicaldisk"
cellcli -e "list physicaldisk where status != normal detail"
cellcli -e "list celldisk"
cellcli -e "list celldisk where status != normal detail"
cellcli -e "list griddisk"
cellcli -e "list griddisk where status != active detail"
cellcli -e "list griddisk attributes name,asmModeStatus,asmDeactivationOutcome"
cellcli -e "list diskmap"

Typical states to check are physical disk normal, cell disk normal, and grid disk active. For ASM, asmModeStatus=ONLINE means ASM is using the grid disk; asmDeactivationOutcome=Yes means it can be deactivated without data loss. Treat that last attribute as status information, not authorization to deactivate a disk. Oracle: Physical disks · Oracle: Grid disks

LIST DISKMAP helps map physical disk slots and serials to cell disks and grid disks. Oracle: LIST

Alerts and cache

cellcli -e "list alerthistory where ageInMinutes < 1440 detail"
cellcli -e "list flashcache detail"
cellcli -e "list flashlog detail"

Alert history includes past alert records; review timestamps, severity, and messages to understand whether an alert is current or historical. Oracle: Alert history

CellCLI syntax tips

LIST <object> [WHERE <filter>] [ATTRIBUTES <attr-list>] [DETAIL]
DESCRIBE <object>
HELP

Examples:

LIST CELLDISK WHERE status != normal ATTRIBUTES name,status,physicalDisk
DESCRIBE GRIDDISK

Commands and object names are generally case-insensitive, and the ending semicolon is optional. DETAIL prints attributes one per line; ATTRIBUTES selects specific fields. Oracle: LIST command

tmux Quick Reference

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DDefault prefix: press Ctrl-b, release it, then press the command key. Example: Ctrl-b, then c. tmux Getting Started

Sessions

tmux new -s work       # Start a named session
tmux ls                # List sessions
tmux attach -t work    # Reattach to a session
tmux kill-session -t work

Ctrl-b d detaches from a session; it keeps running in the background.

Default keys

KeysAction
Ctrl-b cCreate a window
Ctrl-b ,Rename current window
Ctrl-b n / pNext / previous window
Ctrl-b 0–9Select window by number
Ctrl-b wChoose a window
Ctrl-b %Split pane left/right
Ctrl-b "Split pane top/bottom
Ctrl-b + arrowMove to pane in that direction
Ctrl-b oCycle through panes
Ctrl-b zZoom or unzoom current pane
Ctrl-b xClose current pane
Ctrl-b &Close current window
Ctrl-b [Enter copy mode; press q to leave
Ctrl-b dDetach
Ctrl-b ?Show key bindings
Ctrl-b :Open tmux command prompt

Window and pane close commands ask for confirmation. Key bindings can be listed with Ctrl-b ?; the official guide explains the prefix sequence and command prompt. tmux Getting Started

Commands at the tmux prompt

Press Ctrl-b :, type a command, then press Enter.

new-window -n logs
split-window -h          # Left/right panes
split-window -v          # Top/bottom panes
select-window -t :2
select-pane -L           # Or -R, -U, -D
resize-pane -L 5         # Resize by 5 cells

Remember

  • Session: a workspace that can keep running after you detach.
  • Window: like a tab within a session.
  • Pane: a split terminal within a window.
  • Default prefix is Ctrl-b; tmux settings can change it. tmux(1) manual

How to copy a directory and everything inside it while preserving permissions and timestamps

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Use cp -a to copy a directory and everything inside it while preserving permissions and timestamps:

cp -a /path/to/source_dir /path/to/destination/

If the destination directory doesn’t exist, it will be created. To copy only the contents of the source directory into an existing destination:

cp -a /path/to/source_dir/. /path/to/destination/

How to capture network traffic using tcpdump on a Linux machine

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To capture network traffic using tcpdump on a Linux machine and analyze it in Wireshark, follow these steps:

  1. Install Wireshark: If Wireshark is not already installed on your Linux machine, you can install it using your package manager. For example, on Debian-based systems (like Ubuntu), you can use:sudo apt-get update sudo apt-get install wireshark Make sure you have appropriate permissions to run Wireshark or use it with sudo.
  2. Capture network traffic with tcpdump: Run tcpdump to capture the network traffic. For example, to capture all traffic on interface eth0 and save it to a file named capture.pcap:sudo tcpdump -i eth0 -w capture.pcap Replace eth0 with the name of your network interface, which you can find using the ifconfig command.
  3. Stop tcpdump: Once you’ve captured enough traffic, stop tcpdump by pressing Ctrl+C.
  4. Transfer the capture file to your local machine (optional): If you’re running Wireshark on a different machine, you’ll need to transfer the capture file (capture.pcap) from the Linux machine to your local machine. You can use utilities like scp (secure copy) or rsync for this purpose.
  5. Open the capture file in Wireshark: Launch Wireshark on your local machine and open the capture file (capture.pcap) that you created using tcpdump.wireshark capture.pcap Alternatively, you can open Wireshark first and then use the GUI to open the capture file.
  6. Analyze the captured traffic: In Wireshark, you can analyze the captured packets, apply filters, view packet details, and perform various other network analysis tasks.

By following these steps, you can capture network traffic using tcpdump on a Linux machine and analyze it in Wireshark for troubleshooting, security analysis, or network debugging purposes. Remember to use tcpdump with appropriate permissions (e.g., sudo) to capture traffic on privileged ports or interfaces.

Linux: traceroute command

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The traceroute command in Linux is a network diagnostic tool used to trace the path that an Internet Protocol (IP) packet takes from the local machine to a specified destination host. It does this by sending a series of packets with increasing Time-To-Live (TTL) values, starting from 1.

Here’s how the traceroute command works and what information it provides:

  1. Sending packets with TTL: The traceroute command sends UDP packets (by default) or ICMP Echo Request packets towards the destination IP address with TTL set to 1. When a router receives a packet with TTL of 1, it decrements the TTL by 1 and if it reaches zero, it sends back an ICMP “Time Exceeded” message to the sender. This message indicates that the packet has expired.
  2. Analyzing ICMP Time Exceeded messages: traceroute captures these ICMP Time Exceeded messages and uses them to determine the route the packet took to reach the destination. Each router along the path responds with an ICMP Time Exceeded message, indicating its presence.
  3. Incrementing TTL: traceroute then sends another set of packets with TTL set to 2, and so on, until the packets finally reach the destination. Each time, it records the IP address and round-trip time (RTT) of the intermediate routers.
  4. Displaying the route: Once traceroute receives a response from the destination or reaches its maximum number of hops, it displays the route taken by the packets along with the round-trip time for each hop.
  5. Identifying delays: By analyzing the round-trip times, traceroute can identify network delays at each hop, helping to diagnose network performance issues.
  6. Options: The traceroute command supports various options to customize its behavior. For example, you can specify the maximum number of hops (-m option), the type of packets to send (-I for ICMP or -U for UDP), and the interval between packets (-i option).

Example usage:

traceroute google.com

This command would trace the route to google.com, showing the IP addresses of each hop along the way and the round-trip time for each hop.

traceroute is a valuable tool for network troubleshooting, allowing administrators to identify network routing issues, locate bottlenecks, and analyze network performance between two hosts.

Linux: ip route information

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n Linux, the ip route command is used to display and manipulate the kernel’s IP routing table. This table contains information about how packets should be forwarded to their destinations. Here’s a breakdown of the information provided by the ip route command:

  1. Destination: This field represents the destination network or host to which the route applies. It can be specified as an IP address or network address.
  2. Gateway: This field specifies the IP address of the next-hop router to which packets should be forwarded to reach the destination network or host. If the destination is directly reachable (e.g., on the same subnet), this field may be blank.
  3. Genmask/Mask: This field indicates the network mask associated with the destination address. It’s used to determine which portion of the IP address represents the network portion and which portion represents the host portion.
  4. Flags: Flags provide additional information about the route. Common flags include:
    • U (Up): Indicates that the route is up and available.
    • G (Gateway): Indicates that a gateway is required to reach the destination.
    • H (Host): Indicates that the destination is a host (single IP address).
    • D (Dynamic): Indicates that the route was dynamically added by a routing protocol.
    • C (Cache): Indicates that the route was dynamically added and is stored in the routing cache.
    • M (Modified): Indicates that the route has been modified since it was last used.
  5. Metric: This field represents the routing metric associated with the route. The metric is used by the routing algorithm to determine the best path to a destination when multiple routes are available. Lower metric values typically indicate better paths.
  6. Ref: This field shows the number of references to the route. It indicates how many routes are using this particular route entry.
  7. Use: This field displays the number of lookups performed on this route. It indicates how many times this route has been used.
  8. Iface/Interface: This field specifies the network interface through which packets should be sent to reach the destination. It indicates the outgoing interface for the route.
  9. Scope: This field defines the scope of the route, which determines where the route is valid. Common values include:
    • global: The route is valid globally.
    • link: The route is only valid on the local network segment.
    • host: The route is valid only for the specified host.

The ip route command provides a comprehensive view of the system’s routing table, allowing administrators to understand how packets are being routed and to configure routing behavior as needed.

Linux: ifconfig command

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The ifconfig command in Linux (and other Unix-like operating systems) is used to display and configure network interfaces. When you execute the ifconfig command without any arguments, it typically shows information about all active network interfaces on your system. Here’s a breakdown of the data you typically see:

  1. Interface Name (eth0, wlan0, etc.): This is the name of the network interface. It could be a physical interface like Ethernet (eth0, eth1, etc.) or a wireless interface (wlan0, wlan1, etc.).
  2. Link encap: This indicates the type of encapsulation method used on the interface, such as Ethernet, Loopback, or Point-to-Point.
  3. HWaddr (Hardware Address): This is the MAC (Media Access Control) address of the network interface, which uniquely identifies it on the network.
  4. inet: This shows the IPv4 address assigned to the interface. If the interface is configured with an IPv4 address, you’ll see it listed here.
  5. inet6: If IPv6 is enabled on the interface, this field will display the IPv6 address assigned to the interface.
  6. Netmask: This indicates the subnet mask associated with the IPv4 address. It determines the size of the network segment the device is on.
  7. broadcast: This displays the broadcast address for the network segment the interface is connected to. It’s used for broadcasting messages to all devices on the same network.
  8. inet6 addr: Similar to the inet field, but for IPv6 addresses.
  9. Scope: This indicates the scope of the IP address, whether it’s global, link-local, site-local, etc.
  10. RX packets/TX packets: These show the number of packets received (RX) and transmitted (TX) by the interface since it was activated or the statistics were last cleared.
  11. RX bytes/TX bytes: These display the number of bytes received (RX) and transmitted (TX) by the interface.
  12. MTU: This stands for Maximum Transmission Unit, which is the largest packet size allowed on the interface without fragmentation.
  13. RX errors/TX errors: These indicate the number of errors encountered while receiving (RX) or transmitting (TX) packets.
  14. Collisions: This shows the number of collisions detected on the interface. Collisions occur when two devices attempt to transmit data simultaneously on a shared network segment.

The output of ifconfig may vary slightly depending on the version of the tool and the Linux distribution you’re using. Some distributions are moving towards using the ip command instead of ifconfig, as it provides more features and is more powerful.

Linux: display World Wide Port Names (WWPNs)

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To display World Wide Port Names (WWPNs) and other information about Fibre Channel (FC) adapters on a Linux system, you can use various commands depending on the tools available on your system. Here are a few common methods:

  1. Using lsscsi and sg_map commands:This method requires the lsscsi and sg_map utilities, which are commonly available on many Linux distributions.sudo lsscsi -g This command lists SCSI devices, including Fibre Channel adapters. Note down the device corresponding to your Fibre Channel adapter.Then, use sg_map to map SCSI generic (sg) device names to WWPNs:sudo sg_map -i This command will show the mapping of SCSI generic devices to WWPNs and other information.
  2. Using systool:On systems with sysfs support, you can use the systool command to display information about Fibre Channel adapters:sudo systool -c fc_host -v This command lists information about Fibre Channel host adapters, including WWPNs and other details.
  3. Using fcinfo (For systems with Emulex HBAs):If you’re using Emulex HBAs, you can use the fcinfo command:sudo fcinfo <adapter_name> Replace <adapter_name> with the name of your Fibre Channel adapter (e.g., lpfc0). This command will display detailed information about the adapter, including WWPNs.
  4. Using scli (For systems with QLogic HBAs):If you’re using QLogic HBAs, you can use the scli command:sudo scli -p <port_number> -g Replace <port_number> with the port number of your Fibre Channel adapter (e.g., 0). This command will display detailed information about the HBA, including WWPNs.

Choose the method that best fits your system configuration and the tools available. These commands should provide you with the necessary information about WWPNs and other details of your Fibre Channel adapters on Linux.

Linux: How to use nmcli to display current network configuraton and reconfigure a network adapter

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nmcli is a command-line tool used to interact with NetworkManager, a network management daemon used in many Linux distributions. It allows you to view and configure network settings. Here’s how you can use nmcli to display the current network configuration and reconfigure a network adapter:

  1. Display Current Network Configuration:You can use nmcli to display the current network configuration:nmcli connection show This command will list all network connections along with their configuration details.
  2. Display Detailed Information about a Specific Connection:To view detailed information about a specific connection, such as the IP address, gateway, DNS servers, etc., use:nmcli connection show <connection_name> Replace <connection_name> with the name of the connection you want to inspect.
  3. Reconfigure a Network Adapter:To reconfigure a network adapter, you can modify its settings directly using nmcli. Here’s a basic example to set a static IP address:nmcli connection modify <connection_name> ipv4.addresses <ip_address>/<subnet_mask> ipv4.gateway <gateway_address> ipv4.dns <dns_server> Replace <connection_name>, <ip_address>, <subnet_mask>, <gateway_address>, and <dns_server> with appropriate values.For example:nmcli connection modify "Wired Connection 1" ipv4.addresses 192.168.1.100/24 ipv4.gateway 192.168.1.1 ipv4.dns 8.8.8.8 This command modifies the “Wired Connection 1” connection to use the specified static IP address, subnet mask, gateway, and DNS server.
  4. Apply Changes:After modifying the connection settings, apply the changes:nmcli connection up <connection_name> Replace <connection_name> with the name of the connection you modified.
  5. Verify Changes:Use nmcli connection show <connection_name> to verify that the changes have been applied successfully.

Remember to replace placeholders such as <connection_name>, <ip_address>, <subnet_mask>, <gateway_address>, and <dns_server> with actual values relevant to your network configuration. Additionally, ensure that you have appropriate permissions (usually root or sudo) to modify network settings.