How to know what the errno means

Question

When calling execl       I get an errno 2  What does it mean  How can I know the meaning of this errno

User · Accepted Answer

You can use strerror   to get a human-readable string for the error number  This is the same string printed by perror   but it s useful if you re formatting the error message for something other than standard error output   For example    include  lt errno h gt   include  lt string h gt              if read fd  buf  1   -1        printf  Oh dear  something went wrong with read     s n   strerror errno        Linux also supports the explicitly-threadsafe variant strerror r

User · Answer

When you use strace  on Linux  to run your binary  it will output the returns from system calls and what the error number means  This may sometimes be useful to you

User · Answer

On Linux there is also a very neat tool that can tell right away what each error code means  On Ubuntu  apt-get install errno   Then if for example you want to get the description of error type 2  just type errno 2 in the terminal   With errno -l you get a list with all errors and their descriptions  Much easier that other methods mentioned by previous posters

User · Answer

Call  perror  execl      in case of error   Sample   if read fd  buf  1   -1        perror  read        The manpages of errno 3  and perror 3  are interesting  too

User · Answer

Instead of running perror on any error code you get  you can retrieve a complete listing of errno values on your system with the following one-liner   cpp -dM  usr include errno h   grep  define E    sort -n -k 3

User · Answer

Instead of running perror on any error code you get  you can retrieve a complete listing of errno values on your system with the following one-liner   cpp -dM  usr include errno h   grep  define E    sort -n -k 3

User · Answer

Error code 2 means  File Directory not found   In general  you could use the perror function to print a human readable string

User · Answer

Error code 2 means  File Directory not found   In general  you could use the perror function to print a human readable string

User · Answer

I use the following script      usr bin python  import errno import os import sys  toname   dict  str getattr errno  x    x                 for x in dir errno                 if x startswith  E    tocode   dict  x  getattr errno  x                  for x in dir errno                 if x startswith  E     for arg in sys argv 1        if arg in tocode          print arg  tocode arg   os strerror tocode arg       elif arg in toname          print toname arg   arg  os strerror int arg       else          print  Unknown    arg

User · Answer

I use the following script      usr bin python  import errno import os import sys  toname   dict  str getattr errno  x    x                 for x in dir errno                 if x startswith  E    tocode   dict  x  getattr errno  x                  for x in dir errno                 if x startswith  E     for arg in sys argv 1        if arg in tocode          print arg  tocode arg   os strerror tocode arg       elif arg in toname          print toname arg   arg  os strerror int arg       else          print  Unknown    arg

User · Answer

It means      File or Directory not found

User · Answer

include  lt errno h gt    include  lt stdio h gt    include  lt stdlib h gt    int main int i  char  c         if  i    2        fprintf stderr   Usage  perror errno n       else        errno   atoi c 1         perror              exit 0            Works on Solaris  cc perror c -o perror  lt  lt  use this line to compile it

User · Answer

I use the following script      usr bin python  import errno import os import sys  toname   dict  str getattr errno  x    x                 for x in dir errno                 if x startswith  E    tocode   dict  x  getattr errno  x                  for x in dir errno                 if x startswith  E     for arg in sys argv 1        if arg in tocode          print arg  tocode arg   os strerror tocode arg       elif arg in toname          print toname arg   arg  os strerror int arg       else          print  Unknown    arg

User · Answer

Call  perror  execl      in case of error   Sample   if read fd  buf  1   -1        perror  read        The manpages of errno 3  and perror 3  are interesting  too

User · Answer

When you use strace  on Linux  to run your binary  it will output the returns from system calls and what the error number means  This may sometimes be useful to you

User · Answer

Here is the documentation  That should tell you what it means and what to do with them  You should avoid using the numeric value and use the constants listed there as well  as the number may change between different systems

User · Answer

There s a few useful functions for dealing with errnos    Just to make it clear  these are built-in to libc -- I m just providing sample implementations because some people find reading code clearer than reading English     include  lt string h gt  char  strerror int errnum       you can think of it as being implemented like this     static char strerror buf 1024   const char  sys errlist            EPERM      Operation not permitted        ENOENT     No such file or directory        ESRCH      No such process        EINTR      Interrupted system call        EIO        I O error        ENXIO      No such device or address        E2BIG      Argument list too long          etc        int sys nerr   sizeof sys errlist    sizeof char     char  strerror int errnum        if  0  lt   errnum  amp  amp  errnum  lt  sys nerr  amp  amp  sys errlist errnum           strcpy strerror buf  sys errlist errnum        else         sprintf strerror buf   Unknown error  d   errnum       return strerror buf      strerror returns a string describing the error number you ve passed to it   Caution  this is not thread- or interrupt-safe  it is free to rewrite the string and return the same pointer on the next invocation   Use strerror r if you need to worry about that    include  lt stdio h gt  void perror const char  s       you can think of it as being implemented like this     void perror const char  s        fprintf stderr    s   s n   s  strerror errno        perror prints out the message you give it  plus a string describing the current errno  to standard error

User · Answer

This is faster than looking up the code in errno h  shorter than most solutions posted here and it does not require installation of third party tools   perl -E  say    shift  2  yields  No such file or directory

User · Answer

Call  perror  execl      in case of error   Sample   if read fd  buf  1   -1        perror  read        The manpages of errno 3  and perror 3  are interesting  too

User · Answer

Here is the output from errno -l reformatted for readability     1   EPERM             Operation not permitted   2   ENOENT            No such file or directory   3   ESRCH             No such process   4   EINTR             Interrupted system call   5   EIO               Input output error   6   ENXIO             No such device or address   7   E2BIG             Argument list too long   8   ENOEXEC           Exec format error   9   EBADF             Bad file descriptor  10   ECHILD            No child processes  11   EAGAIN            Resource temporarily unavailable  11   EWOULDBLOCK       Resource temporarily unavailable  12   ENOMEM            Cannot allocate memory  13   EACCES            Permission denied  14   EFAULT            Bad address  15   ENOTBLK           Block device required  16   EBUSY             Device or resource busy  17   EEXIST            File exists  18   EXDEV             Invalid cross-device link  19   ENODEV            No such device  20   ENOTDIR           Not a directory  21   EISDIR            Is a directory  22   EINVAL            Invalid argument  23   ENFILE            Too many open files in system  24   EMFILE            Too many open files  25   ENOTTY            Inappropriate ioctl for device  26   ETXTBSY           Text file busy  27   EFBIG             File too large  28   ENOSPC            No space left on device  29   ESPIPE            Illegal seek  30   EROFS             Read-only file system  31   EMLINK            Too many links  32   EPIPE             Broken pipe  33   EDOM              Numerical argument out of domain  34   ERANGE            Numerical result out of range  35   EDEADLK           Resource deadlock avoided  35   EDEADLOCK         Resource deadlock avoided  36   ENAMETOOLONG      File name too long  37   ENOLCK            No locks available  38   ENOSYS            Function not implemented  39   ENOTEMPTY         Directory not empty  40   ELOOP             Too many levels of symbolic links  42   ENOMSG            No message of desired type  43   EIDRM             Identifier removed  44   ECHRNG            Channel number out of range  45   EL2NSYNC          Level 2 not synchronized  46   EL3HLT            Level 3 halted  47   EL3RST            Level 3 reset  48   ELNRNG            Link number out of range  49   EUNATCH           Protocol driver not attached  50   ENOCSI            No CSI structure available  51   EL2HLT            Level 2 halted  52   EBADE             Invalid exchange  53   EBADR             Invalid request descriptor  54   EXFULL            Exchange full  55   ENOANO            No anode  56   EBADRQC           Invalid request code  57   EBADSLT           Invalid slot  59   EBFONT            Bad font file format  60   ENOSTR            Device not a stream  61   ENODATA           No data available  62   ETIME             Timer expired  63   ENOSR             Out of streams resources  64   ENONET            Machine is not on the network  65   ENOPKG            Package not installed  66   EREMOTE           Object is remote  67   ENOLINK           Link has been severed  68   EADV              Advertise error  69   ESRMNT            Srmount error  70   ECOMM             Communication error on send  71   EPROTO            Protocol error  72   EMULTIHOP         Multihop attempted  73   EDOTDOT           RFS specific error  74   EBADMSG           Bad message  75   EOVERFLOW         Value too large for defined data type  76   ENOTUNIQ          Name not unique on network  77   EBADFD            File descriptor in bad state  78   EREMCHG           Remote address changed  79   ELIBACC           Can not access a needed shared library  80   ELIBBAD           Accessing a corrupted shared library  81   ELIBSCN            lib section in a out corrupted  82   ELIBMAX           Attempting to link in too many shared libraries  83   ELIBEXEC          Cannot exec a shared library directly  84   EILSEQ            Invalid or incomplete multibyte or wide character  85   ERESTART          Interrupted system call should be restarted  86   ESTRPIPE          Streams pipe error  87   EUSERS            Too many users  88   ENOTSOCK          Socket operation on non-socket  89   EDESTADDRREQ      Destination address required  90   EMSGSIZE          Message too long  91   EPROTOTYPE        Protocol wrong type for socket  92   ENOPROTOOPT       Protocol not available  93   EPROTONOSUPPORT   Protocol not supported  94   ESOCKTNOSUPPORT   Socket type not supported  95   ENOTSUP           Operation not supported  95   EOPNOTSUPP        Operation not supported  96   EPFNOSUPPORT      Protocol family not supported  97   EAFNOSUPPORT      Address family not supported by protocol  98   EADDRINUSE        Address already in use  99   EADDRNOTAVAIL     Cannot assign requested address 100   ENETDOWN          Network is down 101   ENETUNREACH       Network is unreachable 102   ENETRESET         Network dropped connection on reset 103   ECONNABORTED      Software caused connection abort 104   ECONNRESET        Connection reset by peer 105   ENOBUFS           No buffer space available 106   EISCONN           Transport endpoint is already connected 107   ENOTCONN          Transport endpoint is not connected 108   ESHUTDOWN         Cannot send after transport endpoint shutdown 109   ETOOMANYREFS      Too many references  cannot splice 110   ETIMEDOUT         Connection timed out 111   ECONNREFUSED      Connection refused 112   EHOSTDOWN         Host is down 113   EHOSTUNREACH      No route to host 114   EALREADY          Operation already in progress 115   EINPROGRESS       Operation now in progress 116   ESTALE            Stale file handle 117   EUCLEAN           Structure needs cleaning 118   ENOTNAM           Not a XENIX named type file 119   ENAVAIL           No XENIX semaphores available 120   EISNAM            Is a named type file 121   EREMOTEIO         Remote I O error 122   EDQUOT            Disk quota exceeded 123   ENOMEDIUM         No medium found 124   EMEDIUMTYPE       Wrong medium type 125   ECANCELED         Operation canceled 126   ENOKEY            Required key not available 127   EKEYEXPIRED       Key has expired 128   EKEYREVOKED       Key has been revoked 129   EKEYREJECTED      Key was rejected by service 130   EOWNERDEAD        Owner died 131   ENOTRECOVERABLE   State not recoverable 132   ERFKILL           Operation not possible due to RF-kill 133   EHWPOISON         Memory page has hardware error   I used tabularise in Vim to align the columns     Tab         zs  r1l1l1   Tab                  zs  l1

User · Answer

When you use strace  on Linux  to run your binary  it will output the returns from system calls and what the error number means  This may sometimes be useful to you

User · Answer

There s a few useful functions for dealing with errnos    Just to make it clear  these are built-in to libc -- I m just providing sample implementations because some people find reading code clearer than reading English     include  lt string h gt  char  strerror int errnum       you can think of it as being implemented like this     static char strerror buf 1024   const char  sys errlist            EPERM      Operation not permitted        ENOENT     No such file or directory        ESRCH      No such process        EINTR      Interrupted system call        EIO        I O error        ENXIO      No such device or address        E2BIG      Argument list too long          etc        int sys nerr   sizeof sys errlist    sizeof char     char  strerror int errnum        if  0  lt   errnum  amp  amp  errnum  lt  sys nerr  amp  amp  sys errlist errnum           strcpy strerror buf  sys errlist errnum        else         sprintf strerror buf   Unknown error  d   errnum       return strerror buf      strerror returns a string describing the error number you ve passed to it   Caution  this is not thread- or interrupt-safe  it is free to rewrite the string and return the same pointer on the next invocation   Use strerror r if you need to worry about that    include  lt stdio h gt  void perror const char  s       you can think of it as being implemented like this     void perror const char  s        fprintf stderr    s   s n   s  strerror errno        perror prints out the message you give it  plus a string describing the current errno  to standard error

User · Answer

Instead of running perror on any error code you get  you can retrieve a complete listing of errno values on your system with the following one-liner   cpp -dM  usr include errno h   grep  define E    sort -n -k 3

User · Answer

Call  perror  execl      in case of error   Sample   if read fd  buf  1   -1        perror  read        The manpages of errno 3  and perror 3  are interesting  too

User · Answer

Error code 2 means  File Directory not found   In general  you could use the perror function to print a human readable string

User · Answer

It means      File or Directory not found

User · Answer

I use the following script      usr bin python  import errno import os import sys  toname   dict  str getattr errno  x    x                 for x in dir errno                 if x startswith  E    tocode   dict  x  getattr errno  x                  for x in dir errno                 if x startswith  E     for arg in sys argv 1        if arg in tocode          print arg  tocode arg   os strerror tocode arg       elif arg in toname          print toname arg   arg  os strerror int arg       else          print  Unknown    arg

User · Answer

It means      File or Directory not found

User · Answer

There s a few useful functions for dealing with errnos    Just to make it clear  these are built-in to libc -- I m just providing sample implementations because some people find reading code clearer than reading English     include  lt string h gt  char  strerror int errnum       you can think of it as being implemented like this     static char strerror buf 1024   const char  sys errlist            EPERM      Operation not permitted        ENOENT     No such file or directory        ESRCH      No such process        EINTR      Interrupted system call        EIO        I O error        ENXIO      No such device or address        E2BIG      Argument list too long          etc        int sys nerr   sizeof sys errlist    sizeof char     char  strerror int errnum        if  0  lt   errnum  amp  amp  errnum  lt  sys nerr  amp  amp  sys errlist errnum           strcpy strerror buf  sys errlist errnum        else         sprintf strerror buf   Unknown error  d   errnum       return strerror buf      strerror returns a string describing the error number you ve passed to it   Caution  this is not thread- or interrupt-safe  it is free to rewrite the string and return the same pointer on the next invocation   Use strerror r if you need to worry about that    include  lt stdio h gt  void perror const char  s       you can think of it as being implemented like this     void perror const char  s        fprintf stderr    s   s n   s  strerror errno        perror prints out the message you give it  plus a string describing the current errno  to standard error

User · Answer

include  lt errno h gt    include  lt stdio h gt    include  lt stdlib h gt    int main int i  char  c         if  i    2        fprintf stderr   Usage  perror errno n       else        errno   atoi c 1         perror              exit 0            Works on Solaris  cc perror c -o perror  lt  lt  use this line to compile it

User · Answer

On Linux there is also a very neat tool that can tell right away what each error code means  On Ubuntu  apt-get install errno   Then if for example you want to get the description of error type 2  just type errno 2 in the terminal   With errno -l you get a list with all errors and their descriptions  Much easier that other methods mentioned by previous posters

User · Answer

Type sudo apt-get install moreutils into your shell and then  once that has installed  type errno 2  You can also use errno -l for all error numbers  or see only the file ones by piping it to grep  like this  errno -l   grep file

User · Answer

Here is the documentation  That should tell you what it means and what to do with them  You should avoid using the numeric value and use the constants listed there as well  as the number may change between different systems

User · Answer

This is faster than looking up the code in errno h  shorter than most solutions posted here and it does not require installation of third party tools   perl -E  say    shift  2  yields  No such file or directory

User · Answer

There s a few useful functions for dealing with errnos    Just to make it clear  these are built-in to libc -- I m just providing sample implementations because some people find reading code clearer than reading English     include  lt string h gt  char  strerror int errnum       you can think of it as being implemented like this     static char strerror buf 1024   const char  sys errlist            EPERM      Operation not permitted        ENOENT     No such file or directory        ESRCH      No such process        EINTR      Interrupted system call        EIO        I O error        ENXIO      No such device or address        E2BIG      Argument list too long          etc        int sys nerr   sizeof sys errlist    sizeof char     char  strerror int errnum        if  0  lt   errnum  amp  amp  errnum  lt  sys nerr  amp  amp  sys errlist errnum           strcpy strerror buf  sys errlist errnum        else         sprintf strerror buf   Unknown error  d   errnum       return strerror buf      strerror returns a string describing the error number you ve passed to it   Caution  this is not thread- or interrupt-safe  it is free to rewrite the string and return the same pointer on the next invocation   Use strerror r if you need to worry about that    include  lt stdio h gt  void perror const char  s       you can think of it as being implemented like this     void perror const char  s        fprintf stderr    s   s n   s  strerror errno        perror prints out the message you give it  plus a string describing the current errno  to standard error

User · Answer

Here is the output from errno -l reformatted for readability     1   EPERM             Operation not permitted   2   ENOENT            No such file or directory   3   ESRCH             No such process   4   EINTR             Interrupted system call   5   EIO               Input output error   6   ENXIO             No such device or address   7   E2BIG             Argument list too long   8   ENOEXEC           Exec format error   9   EBADF             Bad file descriptor  10   ECHILD            No child processes  11   EAGAIN            Resource temporarily unavailable  11   EWOULDBLOCK       Resource temporarily unavailable  12   ENOMEM            Cannot allocate memory  13   EACCES            Permission denied  14   EFAULT            Bad address  15   ENOTBLK           Block device required  16   EBUSY             Device or resource busy  17   EEXIST            File exists  18   EXDEV             Invalid cross-device link  19   ENODEV            No such device  20   ENOTDIR           Not a directory  21   EISDIR            Is a directory  22   EINVAL            Invalid argument  23   ENFILE            Too many open files in system  24   EMFILE            Too many open files  25   ENOTTY            Inappropriate ioctl for device  26   ETXTBSY           Text file busy  27   EFBIG             File too large  28   ENOSPC            No space left on device  29   ESPIPE            Illegal seek  30   EROFS             Read-only file system  31   EMLINK            Too many links  32   EPIPE             Broken pipe  33   EDOM              Numerical argument out of domain  34   ERANGE            Numerical result out of range  35   EDEADLK           Resource deadlock avoided  35   EDEADLOCK         Resource deadlock avoided  36   ENAMETOOLONG      File name too long  37   ENOLCK            No locks available  38   ENOSYS            Function not implemented  39   ENOTEMPTY         Directory not empty  40   ELOOP             Too many levels of symbolic links  42   ENOMSG            No message of desired type  43   EIDRM             Identifier removed  44   ECHRNG            Channel number out of range  45   EL2NSYNC          Level 2 not synchronized  46   EL3HLT            Level 3 halted  47   EL3RST            Level 3 reset  48   ELNRNG            Link number out of range  49   EUNATCH           Protocol driver not attached  50   ENOCSI            No CSI structure available  51   EL2HLT            Level 2 halted  52   EBADE             Invalid exchange  53   EBADR             Invalid request descriptor  54   EXFULL            Exchange full  55   ENOANO            No anode  56   EBADRQC           Invalid request code  57   EBADSLT           Invalid slot  59   EBFONT            Bad font file format  60   ENOSTR            Device not a stream  61   ENODATA           No data available  62   ETIME             Timer expired  63   ENOSR             Out of streams resources  64   ENONET            Machine is not on the network  65   ENOPKG            Package not installed  66   EREMOTE           Object is remote  67   ENOLINK           Link has been severed  68   EADV              Advertise error  69   ESRMNT            Srmount error  70   ECOMM             Communication error on send  71   EPROTO            Protocol error  72   EMULTIHOP         Multihop attempted  73   EDOTDOT           RFS specific error  74   EBADMSG           Bad message  75   EOVERFLOW         Value too large for defined data type  76   ENOTUNIQ          Name not unique on network  77   EBADFD            File descriptor in bad state  78   EREMCHG           Remote address changed  79   ELIBACC           Can not access a needed shared library  80   ELIBBAD           Accessing a corrupted shared library  81   ELIBSCN            lib section in a out corrupted  82   ELIBMAX           Attempting to link in too many shared libraries  83   ELIBEXEC          Cannot exec a shared library directly  84   EILSEQ            Invalid or incomplete multibyte or wide character  85   ERESTART          Interrupted system call should be restarted  86   ESTRPIPE          Streams pipe error  87   EUSERS            Too many users  88   ENOTSOCK          Socket operation on non-socket  89   EDESTADDRREQ      Destination address required  90   EMSGSIZE          Message too long  91   EPROTOTYPE        Protocol wrong type for socket  92   ENOPROTOOPT       Protocol not available  93   EPROTONOSUPPORT   Protocol not supported  94   ESOCKTNOSUPPORT   Socket type not supported  95   ENOTSUP           Operation not supported  95   EOPNOTSUPP        Operation not supported  96   EPFNOSUPPORT      Protocol family not supported  97   EAFNOSUPPORT      Address family not supported by protocol  98   EADDRINUSE        Address already in use  99   EADDRNOTAVAIL     Cannot assign requested address 100   ENETDOWN          Network is down 101   ENETUNREACH       Network is unreachable 102   ENETRESET         Network dropped connection on reset 103   ECONNABORTED      Software caused connection abort 104   ECONNRESET        Connection reset by peer 105   ENOBUFS           No buffer space available 106   EISCONN           Transport endpoint is already connected 107   ENOTCONN          Transport endpoint is not connected 108   ESHUTDOWN         Cannot send after transport endpoint shutdown 109   ETOOMANYREFS      Too many references  cannot splice 110   ETIMEDOUT         Connection timed out 111   ECONNREFUSED      Connection refused 112   EHOSTDOWN         Host is down 113   EHOSTUNREACH      No route to host 114   EALREADY          Operation already in progress 115   EINPROGRESS       Operation now in progress 116   ESTALE            Stale file handle 117   EUCLEAN           Structure needs cleaning 118   ENOTNAM           Not a XENIX named type file 119   ENAVAIL           No XENIX semaphores available 120   EISNAM            Is a named type file 121   EREMOTEIO         Remote I O error 122   EDQUOT            Disk quota exceeded 123   ENOMEDIUM         No medium found 124   EMEDIUMTYPE       Wrong medium type 125   ECANCELED         Operation canceled 126   ENOKEY            Required key not available 127   EKEYEXPIRED       Key has expired 128   EKEYREVOKED       Key has been revoked 129   EKEYREJECTED      Key was rejected by service 130   EOWNERDEAD        Owner died 131   ENOTRECOVERABLE   State not recoverable 132   ERFKILL           Operation not possible due to RF-kill 133   EHWPOISON         Memory page has hardware error   I used tabularise in Vim to align the columns     Tab         zs  r1l1l1   Tab                  zs  l1

User · Answer

It means      File or Directory not found

User · Answer

Here is the documentation  That should tell you what it means and what to do with them  You should avoid using the numeric value and use the constants listed there as well  as the number may change between different systems

User · Answer

When you use strace  on Linux  to run your binary  it will output the returns from system calls and what the error number means  This may sometimes be useful to you

User · Answer

Instead of running perror on any error code you get  you can retrieve a complete listing of errno values on your system with the following one-liner   cpp -dM  usr include errno h   grep  define E    sort -n -k 3

User · Answer

I have the following function in my  bashrc file - it looks up the errno value from the header files  can be either  usr include errno h   usr include linux errno h  etc   etc    It works if header files are installed on the machine -   Usually the header file have an error   next comes the explanation in the comment  something of the following     asm-generic errno-base h  define      EAGAIN          11         Try again     function errno         local arg  1      if     x arg      x-h      then         cat  lt  lt EOF         Usage  errno  lt num gt          Prints text that describes errno error number         EOF     else         pushd  usr include         find   -name  errno  h    xargs grep       space     arg    space             popd     fi

User · Answer

Error code 2 means  File Directory not found   In general  you could use the perror function to print a human readable string

User · Answer

I have the following function in my  bashrc file - it looks up the errno value from the header files  can be either  usr include errno h   usr include linux errno h  etc   etc    It works if header files are installed on the machine -   Usually the header file have an error   next comes the explanation in the comment  something of the following     asm-generic errno-base h  define      EAGAIN          11         Try again     function errno         local arg  1      if     x arg      x-h      then         cat  lt  lt EOF         Usage  errno  lt num gt          Prints text that describes errno error number         EOF     else         pushd  usr include         find   -name  errno  h    xargs grep       space     arg    space             popd     fi

User · Answer

Here is the documentation  That should tell you what it means and what to do with them  You should avoid using the numeric value and use the constants listed there as well  as the number may change between different systems

User · Answer

Type sudo apt-get install moreutils into your shell and then  once that has installed  type errno 2  You can also use errno -l for all error numbers  or see only the file ones by piping it to grep  like this  errno -l   grep file

[c] How to know what the 'errno' means?

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