debug Namespace

The debug API gives you access to several non-standard RPC methods, which will allow you to inspect, debug and set certain debugging flags during runtime.

debug_backtraceAt

Sets the logging backtrace location. When a backtrace location is set and a log message is emitted at that location, the stack of the goroutine executing the log statement will be printed to stderr.

The location is specified as <filename>:<line>.

Client Method invocation
Console debug.backtraceAt(string)
RPC {"method": "debug_backtraceAt", "params": [string]}

Example:

> debug.backtraceAt("server.go:443")

debug_blockProfile

Turns on block profiling for the given duration and writes profile data to disk. It uses a profile rate of 1 for most accurate information. If a different rate is desired, set the rate and write the profile manually using debug_writeBlockProfile.

Client Method invocation
Console debug.blockProfile(file, seconds)
RPC {"method": "debug_blockProfile", "params": [string, number]}

debug_cpuProfile

Turns on CPU profiling for the given duration and writes profile data to disk.

Client Method invocation
Console debug.cpuProfile(file, seconds)
RPC {"method": "debug_cpuProfile", "params": [string, number]}

debug_dumpBlock

Retrieves the state that corresponds to the block number and returns a list of accounts (including storage and code).

Client Method invocation
Go debug.DumpBlock(number uint64) (state.World, error)
Console debug.traceBlockByHash(number, [options])
RPC {"method": "debug_dumpBlock", "params": [number]}

Example

> debug.dumpBlock(10)
{
    fff7ac99c8e4feb60c9750054bdc14ce1857f181: {
      balance: "49358640978154672",
      code: "",
      codeHash: "c5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470",
      nonce: 2,
      root: "56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
      storage: {}
    },
    fffbca3a38c3c5fcb3adbb8e63c04c3e629aafce: {
      balance: "3460945928",
      code: "",
      codeHash: "c5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470",
      nonce: 657,
      root: "56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421",
      storage: {}
    }
  },
  root: "19f4ed94e188dd9c7eb04226bd240fa6b449401a6c656d6d2816a87ccaf206f1"
}

debug_gcStats

Returns GC statistics.

See https://golang.org/pkg/runtime/debug/#GCStats for information about the fields of the returned object.

Client Method invocation
Console debug.gcStats()
RPC {"method": "debug_gcStats", "params": []}

debug_getBlockRlp

Retrieves and returns the RLP encoded block by number.

Client Method invocation
Go debug.GetBlockRlp(number uint64) (string, error)
Console debug.getBlockRlp(number, [options])
RPC {"method": "debug_getBlockRlp", "params": [number]}

References: RLP

debug_goTrace

Turns on Go runtime tracing for the given duration and writes trace data to disk.

Client Method invocation
Console debug.goTrace(file, seconds)
RPC {"method": "debug_goTrace", "params": [string, number]}

debug_memStats

Returns detailed runtime memory statistics.

See https://golang.org/pkg/runtime/#MemStats for information about the fields of the returned object.

Client Method invocation
Console debug.memStats()
RPC {"method": "debug_memStats", "params": []}

debug_seedHash

Fetches and retrieves the seed hash of the block by number

Client Method invocation
Go debug.SeedHash(number uint64) (string, error)
Console debug.seedHash(number, [options])
RPC {"method": "debug_seedHash", "params": [number]}

debug_setHead

Sets the current head of the local chain by block number. Note, this is a destructive action and may severely damage your chain. Use with extreme caution.

Client Method invocation
Go debug.SetHead(number uint64)
Console debug.setHead(number)
RPC {"method": "debug_setHead", "params": [number]}

References: Ethash

debug_setBlockProfileRate

Sets the rate (in samples/sec) of goroutine block profile data collection. A non-zero rate enables block profiling, setting it to zero stops the profile. Collected profile data can be written using debug_writeBlockProfile.

Client Method invocation
Console debug.setBlockProfileRate(rate)
RPC {"method": "debug_setBlockProfileRate", "params": [number]}

debug_stacks

Returns a printed representation of the stacks of all goroutines. Note that the web3 wrapper for this method takes care of the printing and does not return the string.

Client Method invocation
Console debug.stacks()
RPC {"method": "debug_stacks", "params": []}

debug_startCPUProfile

Turns on CPU profiling indefinitely, writing to the given file.

Client Method invocation
Console debug.startCPUProfile(file)
RPC {"method": "debug_startCPUProfile", "params": [string]}

debug_startGoTrace

Starts writing a Go runtime trace to the given file.

Client Method invocation
Console debug.startGoTrace(file)
RPC {"method": "debug_startGoTrace", "params": [string]}

debug_stopCPUProfile

Stops an ongoing CPU profile.

Client Method invocation
Console debug.stopCPUProfile()
RPC {"method": "debug_stopCPUProfile", "params": []}

debug_stopGoTrace

Stops writing the Go runtime trace.

Client Method invocation
Console debug.startGoTrace(file)
RPC {"method": "debug_stopGoTrace", "params": []}

debug_traceBlock

The traceBlock method will return a full stack trace of all invoked opcodes of all transaction that were included included in this block. Note, the parent of this block must be present or it will fail.

Client Method invocation
Go debug.TraceBlock(blockRlp []byte, config. *vm.Config) BlockTraceResult
Console debug.traceBlock(tblockRlp, [options])
RPC {"method": "debug_traceBlock", "params": [blockRlp, {}]}

References: RLP

Example

> debug.traceBlock("0xblock_rlp")
{
  gas: 85301,
  returnValue: "",
  structLogs: [{
      depth: 1,
      error: "",
      gas: 162106,
      gasCost: 3,
      memory: null,
      op: "PUSH1",
      pc: 0,
      stack: [],
      storage: {}
  },
    /* snip */
  {
      depth: 1,
      error: "",
      gas: 100000,
      gasCost: 0,
      memory: ["0000000000000000000000000000000000000000000000000000000000000006", "0000000000000000000000000000000000000000000000000000000000000000", "0000000000000000000000000000000000000000000000000000000000000060"],
      op: "STOP",
      pc: 120,
      stack: ["00000000000000000000000000000000000000000000000000000000d67cbec9"],
      storage: {
        0000000000000000000000000000000000000000000000000000000000000004: "8241fa522772837f0d05511f20caa6da1d5a3209000000000000000400000001",
        0000000000000000000000000000000000000000000000000000000000000006: "0000000000000000000000000000000000000000000000000000000000000001",
        f652222313e28459528d920b65115c16c04f3efc82aaedc97be59f3f377c0d3f: "00000000000000000000000002e816afc1b5c0f39852131959d946eb3b07b5ad"
      }
  }]

debug_traceBlockByNumber

Similar to debug_traceBlock, traceBlockByNumber accepts a block number and will replay the block that is already present in the database.

Client Method invocation
Go debug.TraceBlockByNumber(number uint64, config. *vm.Config) BlockTraceResult
Console debug.traceBlockByNumber(number, [options])
RPC {"method": "debug_traceBlockByNumber", "params": [number, {}]}

References: RLP

debug_traceBlockByHash

Similar to debug_traceBlock, traceBlockByHash accepts a block hash and will replay the block that is already present in the database.

Client Method invocation
Go debug.TraceBlockByHash(hash common.Hash, config. *vm.Config) BlockTraceResult
Console debug.traceBlockByHash(hash, [options])
RPC {"method": "debug_traceBlockByHash", "params": [hash {}]}

References: RLP

debug_traceBlockFromFile

Similar to debug_traceBlock, traceBlockFromFile accepts a file containing the RLP of the block.

Client Method invocation
Go debug.TraceBlockFromFile(fileName string, config. *vm.Config) BlockTraceResult
Console debug.traceBlockFromFile(fileName, [options])
RPC {"method": "debug_traceBlockFromFile", "params": [fileName, {}]}

References: RLP

debug_standardTraceBlockToFile

When JS-based tracing (see below) was first implemented, the intended usecase was to enable long-running tracers that could stream results back via a subscription channel. This method works a bit differently. (For full details, see PR)

  • It streams output to disk during the execution, to not blow up the memory usage on the node
  • It uses jsonl as output format (to allow streaming)
  • Uses a cross-client standardized output, so called ‘standard json’
    • Uses op for string-representation of opcode, instead of op/opName for numeric/string, and other simlar small differences.
    • has refund
    • Represents memory as a contiguous chunk of data, as opposed to a list of 32-byte segments like debug_traceTransaction

This means that this method is only ‘useful’ for callers who control the node – at least sufficiently to be able to read the artefacts from the filesystem after the fact.

The method can be used to dump a certain transaction out of a given block:

> debug.standardTraceBlockToFile("0x0bbe9f1484668a2bf159c63f0cf556ed8c8282f99e3ffdb03ad2175a863bca63", {txHash:"0x4049f61ffbb0747bb88dc1c85dd6686ebf225a3c10c282c45a8e0c644739f7e9", disableMemory:true})
["/tmp/block_0x0bbe9f14-14-0x4049f61f-099048234"]

Or all txs from a block:

> debug.standardTraceBlockToFile("0x0bbe9f1484668a2bf159c63f0cf556ed8c8282f99e3ffdb03ad2175a863bca63", {disableMemory:true})
["/tmp/block_0x0bbe9f14-0-0xb4502ea7-409046657", "/tmp/block_0x0bbe9f14-1-0xe839be8f-954614764", "/tmp/block_0x0bbe9f14-2-0xc6e2052f-542255195", "/tmp/block_0x0bbe9f14-3-0x01b7f3fe-209673214", "/tmp/block_0x0bbe9f14-4-0x0f290422-320999749", "/tmp/block_0x0bbe9f14-5-0x2dc0fb80-844117472", "/tmp/block_0x0bbe9f14-6-0x35542da1-256306111", "/tmp/block_0x0bbe9f14-7-0x3e199a08-086370834", "/tmp/block_0x0bbe9f14-8-0x87778b88-194603593", "/tmp/block_0x0bbe9f14-9-0xbcb081ba-629580052", "/tmp/block_0x0bbe9f14-10-0xc254381a-578605923", "/tmp/block_0x0bbe9f14-11-0xcc434d58-405931366", "/tmp/block_0x0bbe9f14-12-0xce61967d-874423181", "/tmp/block_0x0bbe9f14-13-0x05a20b35-267153288", "/tmp/block_0x0bbe9f14-14-0x4049f61f-606653767", "/tmp/block_0x0bbe9f14-15-0x46d473d2-614457338", "/tmp/block_0x0bbe9f14-16-0x35cf5500-411906321", "/tmp/block_0x0bbe9f14-17-0x79222961-278569788", "/tmp/block_0x0bbe9f14-18-0xad84e7b1-095032683", "/tmp/block_0x0bbe9f14-19-0x4bd48260-019097038", "/tmp/block_0x0bbe9f14-20-0x1517411d-292624085", "/tmp/block_0x0bbe9f14-21-0x6857e350-971385904", "/tmp/block_0x0bbe9f14-22-0xbe3ae2ca-236639695"]

Files are created in a temp-location, with the naming standard block_<blockhash:4>-<txindex>-<txhash:4>-<random suffix>. Each opcode immediately streams to file, with no in-geth buffering aside from whatever buffering the os normally does.

On the server side, it also adds some more info when regenerating historical state, namely, the reexec-number if required historical state is not avaiable is encountered, so a user can experiment with increasing that setting. It also prints out the remaining block until it reaches target:

INFO [10-15|13:48:25.263] Regenerating historical state            block=2385959 target=2386012 remaining=53   elapsed=3m30.990537767s
INFO [10-15|13:48:33.342] Regenerating historical state            block=2386012 target=2386012 remaining=0    elapsed=3m39.070073163s
INFO [10-15|13:48:33.343] Historical state regenerated             block=2386012 elapsed=3m39.070454362s nodes=10.03mB preimages=652.08kB
INFO [10-15|13:48:33.352] Wrote trace                              file=/tmp/block_0x14490c57-0-0xfbbd6d91-715824834
INFO [10-15|13:48:33.352] Wrote trace                              file=/tmp/block_0x14490c57-1-0x71076194-187462969
INFO [10-15|13:48:34.421] Wrote trace file=/tmp/block_0x14490c57-2-0x3f4263fe-056924484

The options is as follows:

type StdTraceConfig struct {
  *vm.LogConfig
  Reexec *uint64
  TxHash *common.Hash
}

debug_standardTraceBadBlockToFile

This method is similar to debug_standardTraceBlockToFile, but can be used to obtain info about a block which has been rejected as invalid (for some reason).

debug_traceTransaction

OBS In most scenarios, debug.standardTraceBlockToFile is better suited for tracing!

The traceTransaction debugging method will attempt to run the transaction in the exact same manner as it was executed on the network. It will replay any transaction that may have been executed prior to this one before it will finally attempt to execute the transaction that corresponds to the given hash.

In addition to the hash of the transaction you may give it a secondary optional argument, which specifies the options for this specific call. The possible options are:

  • disableStorage: BOOL. Setting this to true will disable storage capture (default = false).
  • disableMemory: BOOL. Setting this to true will disable memory capture (default = false).
  • disableStack: BOOL. Setting this to true will disable stack capture (default = false).
  • tracer: STRING. Setting this will enable JavaScript-based transaction tracing, described below. If set, the previous four arguments will be ignored.
  • timeout: STRING. Overrides the default timeout of 5 seconds for JavaScript-based tracing calls. Valid values are described here.
Client Method invocation
Go debug.TraceTransaction(txHash common.Hash, logger *vm.LogConfig) (*ExecutionResurt, error)
Console debug.traceTransaction(txHash, [options])
RPC {"method": "debug_traceTransaction", "params": [txHash, {}]}

Example

> debug.traceTransaction("0x2059dd53ecac9827faad14d364f9e04b1d5fe5b506e3acc886eff7a6f88a696a")
{
  gas: 85301,
  returnValue: "",
  structLogs: [{
      depth: 1,
      error: "",
      gas: 162106,
      gasCost: 3,
      memory: null,
      op: "PUSH1",
      pc: 0,
      stack: [],
      storage: {}
  },
    /* snip */
  {
      depth: 1,
      error: "",
      gas: 100000,
      gasCost: 0,
      memory: ["0000000000000000000000000000000000000000000000000000000000000006", "0000000000000000000000000000000000000000000000000000000000000000", "0000000000000000000000000000000000000000000000000000000000000060"],
      op: "STOP",
      pc: 120,
      stack: ["00000000000000000000000000000000000000000000000000000000d67cbec9"],
      storage: {
        0000000000000000000000000000000000000000000000000000000000000004: "8241fa522772837f0d05511f20caa6da1d5a3209000000000000000400000001",
        0000000000000000000000000000000000000000000000000000000000000006: "0000000000000000000000000000000000000000000000000000000000000001",
        f652222313e28459528d920b65115c16c04f3efc82aaedc97be59f3f377c0d3f: "00000000000000000000000002e816afc1b5c0f39852131959d946eb3b07b5ad"
      }
  }]

JavaScript-based tracing

Specifying the tracer option in the second argument enables JavaScript-based tracing. In this mode, tracer is interpreted as a JavaScript expression that is expected to evaluate to an object with (at least) two methods, named step and result.

stepis a function that takes two arguments, log and db, and is called for each step of the EVM, or when an error occurs, as the specified transaction is traced.

log has the following fields:

  • pc: Number, the current program counter
  • op: Object, an OpCode object representing the current opcode
  • gas: Number, the amount of gas remaining
  • gasPrice: Number, the cost in wei of each unit of gas
  • memory: Object, a structure representing the contract’s memory space
  • stack: array[big.Int], the EVM execution stack
  • depth: The execution depth
  • account: The address of the account executing the current operation
  • err: If an error occured, information about the error

If err is non-null, all other fields should be ignored.

For efficiency, the same log object is reused on each execution step, updated with current values; make sure to copy values you want to preserve beyond the current call. For instance, this step function will not work:

function(log) {
  this.logs.append(log);
}

But this step function will:

function(log) {
  this.logs.append({gas: log.gas, pc: log.pc, ...});
}

log.op has the following methods:

  • isPush() - returns true iff the opcode is a PUSHn
  • toString() - returns the string representation of the opcode
  • toNumber() - returns the opcode’s number

log.memory has the following methods:

  • slice(start, stop) - returns the specified segment of memory as a byte slice
  • length() - returns the length of the memory

log.stack has the following methods:

  • peek(idx) - returns the idx-th element from the top of the stack (0 is the topmost element) as a big.Int
  • length() - returns the number of elements in the stack

db has the following methods:

  • getBalance(address) - returns a big.Int with the specified account’s balance
  • getNonce(address) - returns a Number with the specified account’s nonce
  • getCode(address) - returns a byte slice with the code for the specified account
  • getState(address, hash) - returns the state value for the specified account and the specified hash
  • exists(address) - returns true if the specified address exists

The second function, ‘result’, takes no arguments, and is expected to return a JSON-serializable value to return to the RPC caller.

If the step function throws an exception or executes an illegal operation at any point, it will not be called on any further VM steps, and the error will be returned to the caller.

Note that several values are Golang big.Int objects, not JavaScript numbers or JS bigints. As such, they have the same interface as described in the godocs. Their default serialization to JSON is as a Javascript number; to serialize large numbers accurately call .String() on them. For convenience, big.NewInt(x) is provided, and will convert a uint to a Go BigInt.

Usage example, returns the top element of the stack at each CALL opcode only:

debug.traceTransaction(txhash, {tracer: '{data: [], fault: function(log) {}, step: function(log) { if(log.op.toString() == "CALL") this.data.push(log.stack.peek(0)); }, result: function() { return this.data; }}'});

debug_verbosity

Sets the logging verbosity ceiling. Log messages with level up to and including the given level will be printed.

The verbosity of individual packages and source files can be raised using debug_vmodule.

Client Method invocation
Console debug.verbosity(level)
RPC {"method": "debug_vmodule", "params": [number]}

debug_vmodule

Sets the logging verbosity pattern.

Client Method invocation
Console debug.vmodule(string)
RPC {"method": "debug_vmodule", "params": [string]}

Examples

If you want to see messages from a particular Go package (directory) and all subdirectories, use:

> debug.vmodule("eth/*=6")

If you want to restrict messages to a particular package (e.g. p2p) but exclude subdirectories, use:

> debug.vmodule("p2p=6")

If you want to see log messages from a particular source file, use

> debug.vmodule("server.go=6")

You can compose these basic patterns. If you want to see all output from peer.go in a package below eth (eth/peer.go, eth/downloader/peer.go) as well as output from package p2p at level <= 5, use:

debug.vmodule("eth/*/peer.go=6,p2p=5")

debug_writeBlockProfile

Writes a goroutine blocking profile to the given file.

Client Method invocation
Console debug.writeBlockProfile(file)
RPC {"method": "debug_writeBlockProfile", "params": [string]}

debug_writeMemProfile

Writes an allocation profile to the given file. Note that the profiling rate cannot be set through the API, it must be set on the command line using the --memprofilerate flag.

Client Method invocation
Console debug.writeMemProfile(file string)
RPC {"method": "debug_writeBlockProfile", "params": [string]}