make oldconfig error

You'll install the gcc compiler package + your Distro's equivalent of the build-essential package (if it's not installed).

You must have gcc installed before you can build much of anything... especially the entire Kernel...

Building Kernels is complex.

Having a Kernel Crash can lose a great deal of data.

Debugging Kernel Crashes after custom builds can eat up a massive amount of time.

Tip: Rather than building the 5.0 Kernel on Bionic, might be good to wait 10 days till Focal releases, then you'll have a 5.4 version of the Kernel installed by default.

i did

lnxvm@lnxvm-VirtualBox:/$ sudo apt-get install manpages-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
manpages-dev is already the newest version (4.15-1).
manpages-dev set to manually installed.
The following packages were automatically installed and are no longer required:
  fonts-liberation2 fonts-opensymbol gir1.2-geocodeglib-1.0 gir1.2-gst-plugins-base-1.0 gir1.2-gstreamer-1.0 gir1.2-gudev-1.0
  gir1.2-udisks-2.0 grilo-plugins-0.3-base gstreamer1.0-gtk3 libboost-date-time1.65.1 libboost-filesystem1.65.1
  libboost-iostreams1.65.1 libboost-locale1.65.1 libcdr-0.1-1 libclucene-contribs1v5 libclucene-core1v5 libcmis-0.5-5v5 libcolamd2
  libdazzle-1.0-0 libe-book-0.1-1 libedataserverui-1.2-2 libeot0 libepubgen-0.1-1 libetonyek-0.1-1 libevent-2.1-6 libexiv2-14
  libfreerdp-client2-2 libfreerdp2-2 libgc1c2 libgee-0.8-2 libgexiv2-2 libgom-1.0-0 libgpgmepp6 libgpod-common libgpod4
  liblangtag-common liblangtag1 liblirc-client0 liblua5.3-0 libmediaart-2.0-0 libmspub-0.1-1 libodfgen-0.1-1 libqqwing2v5 libraw16
  librevenge-0.0-0 libsgutils2-2 libssh-4 libsuitesparseconfig5 libvncclient1 libwinpr2-2 libxapian30 libxmlsec1 libxmlsec1-nss
  lp-solve media-player-info python3-mako python3-markupsafe syslinux syslinux-common syslinux-legacy usb-creator-common
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 282 not upgraded.
lnxvm@lnxvm-VirtualBox:/$ gcc --version
gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


am geting
lnxvm@lnxvm-VirtualBox:/usr/src/kernel/linux-5.6.3$ make menuconfig
  HOSTCC  scripts/basic/fixdep
  UPD     scripts/kconfig/mconf-cfg
  HOSTCC  scripts/kconfig/mconf.o
  HOSTCC  scripts/kconfig/lxdialog/checklist.o
  HOSTCC  scripts/kconfig/lxdialog/inputbox.o
  HOSTCC  scripts/kconfig/lxdialog/menubox.o
  HOSTCC  scripts/kconfig/lxdialog/textbox.o
  HOSTCC  scripts/kconfig/lxdialog/util.o
  HOSTCC  scripts/kconfig/lxdialog/yesno.o
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  LEX     scripts/kconfig/lexer.lex.c
/bin/sh: 1: flex: not found
scripts/Makefile.host:9: recipe for target 'scripts/kconfig/lexer.lex.c' failed
make[1]: *** [scripts/kconfig/lexer.lex.c] Error 127
Makefile:568: recipe for target 'menuconfig' failed
make: *** [menuconfig] Error 2

@chalie001

I am trying the same at localhost vmplayer
1)
downloaded
https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.6.3.tar.xz
2)
at Linux CentOS 5.5

$ make oldconfig
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/kconfig/conf.o
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  LEX     scripts/kconfig/lexer.lex.c
/bin/sh: flex: command not found
$ sudo yum -y install flex

Select allOpen in new window

flex installation used to take time.

@chalie001

I like the comment from David Favor
>> Building Kernels is complex.
>> Having a Kernel Crash can lose a great deal of data.
Hence better have a backup before proceeding the same.

I am unable to reproduce your error
for your information:

$ yum list > ~/svn/yum_list.txt
$ grep "^gcc" ~/svn/yum_list.txt
gcc.x86_64                                   4.1.2-55.el5             installed
gcc-c++.x86_64                               4.1.2-55.el5             installed
gcc44.x86_64                                 4.4.7-11.el5_11          installed
gcc44-c++.x86_64                             4.4.7-11.el5_11          installed
gcc.x86_64                                   4.8.5-39.0.3.el7         ol7_latest
gcc-c++.x86_64                               4.8.5-39.0.3.el7         ol7_latest
gcc-gfortran.x86_64                          4.8.5-39.0.3.el7         ol7_latest
gcc-gnat.x86_64                              4.8.5-39.0.3.el7         ol7_latest
gcc-java.x86_64                              4.1.2-55.el5             el5_latest
gcc-objc.x86_64                              4.8.5-39.0.3.el7         ol7_latest
gcc-objc++.x86_64                            4.8.5-39.0.3.el7         ol7_latest
gcc44-gfortran.x86_64                        4.4.7-11.el5_11          el5_latest
$ grep "flex" ~/svn/yum_list.txt
flex.x86_64                                  2.5.37-6.el7             ol7_latest

Select allOpen in new window

sudo yum -y install flex.x86_64
sudo yum -y install gcc.x86_64
sudo yum -y install gcc-c++.x86_64
sudo yum -y install gcc-gfortran.x86_64
sudo yum -y install gcc-gnat.x86_64
sudo yum -y install gcc-objc.x86_64
sudo yum -y install gcc-objc++.x86_64

Select allOpen in new window

The top-level README in the Linux source tree is very short and you should have read it before starting.
It directs you to first read Documentation/admin-guide/README.rst
That file in turn advises you read Documentation/process/changes.rst for a comprehensive list of software required to build the kernel, with how to check what is installed now.
I am not posting a copy here - you can read it for yourself - but flex is the 4th entry in the list.

https://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D provides another option.

This is where all Ubuntu Kernel builds live, before they're rolled into Distros.

You can even download a prebuild 5.6.4 + even a 5.7 Beta Kernel from this archive.

am in ubuntu i did

sudo apt-get -y install flex
Reading package lists... Done
Building dependency tree      
Reading state information... Done
The following packages were automatically installed and are no longer required:
  fonts-liberation2 fonts-opensymbol gir1.2-geocodeglib-1.0
  gir1.2-gst-plugins-base-1.0 gir1.2-gstreamer-1.0 gir1.2-gudev-1.0
  gir1.2-udisks-2.0 grilo-plugins-0.3-base gstreamer1.0-gtk3
  libboost-date-time1.65.1 libboost-filesystem1.65.1 libboost-iostreams1.65.1
  libboost-locale1.65.1 libcdr-0.1-1 libclucene-contribs1v5
  libclucene-core1v5 libcmis-0.5-5v5 libcolamd2 libdazzle-1.0-0
  libe-book-0.1-1 libedataserverui-1.2-2 libeot0 libepubgen-0.1-1
  libetonyek-0.1-1 libevent-2.1-6 libexiv2-14 libfreerdp-client2-2
  libfreerdp2-2 libgc1c2 libgee-0.8-2 libgexiv2-2 libgom-1.0-0 libgpgmepp6
  libgpod-common libgpod4 liblangtag-common liblangtag1 liblirc-client0
  liblua5.3-0 libmediaart-2.0-0 libmspub-0.1-1 libodfgen-0.1-1 libqqwing2v5
  libraw16 librevenge-0.0-0 libsgutils2-2 libssh-4 libsuitesparseconfig5
  libvncclient1 libwinpr2-2 libxapian30 libxmlsec1 libxmlsec1-nss lp-solve
  media-player-info python3-mako python3-markupsafe syslinux syslinux-common
  syslinux-legacy usb-creator-common
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  libfl-dev libfl2 libsigsegv2 m4
Suggested packages:
  bison flex-doc m4-doc
The following NEW packages will be installed:
  flex libfl-dev libfl2 libsigsegv2 m4
0 upgraded, 5 newly installed, 0 to remove and 284 not upgraded.
Need to get 545 kB of archives.
After this operation, 1,511 kB of additional disk space will be used.
Get:1 http://za.archive.ubuntu.com/ubuntu bionic/main amd64 libsigsegv2 amd64 2.12-1 [14.7 kB]
Get:2 http://za.archive.ubuntu.com/ubuntu bionic/main amd64 m4 amd64 1.4.18-1 [197 kB]
Get:3 http://za.archive.ubuntu.com/ubuntu bionic/main amd64 flex amd64 2.6.4-6 [316 kB]
Get:4 http://za.archive.ubuntu.com/ubuntu bionic/main amd64 libfl2 amd64 2.6.4-6 [11.4 kB]
Get:5 http://za.archive.ubuntu.com/ubuntu bionic/main amd64 libfl-dev amd64 2.6.4-6 [6,320 B]
Fetched 545 kB in 1s (418 kB/s)
Selecting previously unselected package libsigsegv2:amd64.
(Reading database ... 122333 files and directories currently installed.)
Preparing to unpack .../libsigsegv2_2.12-1_amd64.deb ...
Unpacking libsigsegv2:amd64 (2.12-1) ...
Selecting previously unselected package m4.
Preparing to unpack .../archives/m4_1.4.18-1_amd64.deb ...
Unpacking m4 (1.4.18-1) ...
Selecting previously unselected package flex.
Preparing to unpack .../flex_2.6.4-6_amd64.deb ...
Unpacking flex (2.6.4-6) ...
Selecting previously unselected package libfl2:amd64.
Preparing to unpack .../libfl2_2.6.4-6_amd64.deb ...
Unpacking libfl2:amd64 (2.6.4-6) ...
Selecting previously unselected package libfl-dev:amd64.
Preparing to unpack .../libfl-dev_2.6.4-6_amd64.deb ...
Unpacking libfl-dev:amd64 (2.6.4-6) ...
Setting up libsigsegv2:amd64 (2.12-1) ...
Processing triggers for install-info (6.5.0.dfsg.1-2) ...
Setting up m4 (1.4.18-1) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Setting up libfl2:amd64 (2.6.4-6) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Setting up flex (2.6.4-6) ...
Setting up libfl-dev:amd64 (2.6.4-6) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
lnxvm@lnxvm-VirtualBox:/usr/src/kernel$ make oldconfig
make: *** No rule to make target 'oldconfig'.  Stop.
lnxvm@lnxvm-VirtualBox:/usr/src/kernel$ make menuconfig
make: *** No rule to make target 'menuconfig'.  Stop.

From the output you posted, you will need bison soon enough. But let's get your source directory sorted out first.

i did

lnxvm@lnxvm-VirtualBox:/usr/src/kernel/linux-5.6.3$ ls -ltr
total 808
drwxrwxr-x   4 lnxvm lnxvm   4096 Apr  8 09:11 virt
drwxrwxr-x   3 lnxvm lnxvm   4096 Apr  8 09:11 usr
drwxrwxr-x  36 lnxvm lnxvm   4096 Apr  8 09:11 tools
drwxrwxr-x  26 lnxvm lnxvm   4096 Apr  8 09:11 sound
drwxrwxr-x  12 lnxvm lnxvm   4096 Apr  8 09:11 security
drwxrwxr-x  15 lnxvm lnxvm   4096 Apr  8 09:11 scripts
drwxrwxr-x  30 lnxvm lnxvm   4096 Apr  8 09:11 samples
-rw-rw-r--   1 lnxvm lnxvm    727 Apr  8 09:11 README
drwxrwxr-x  72 lnxvm lnxvm   4096 Apr  8 09:11 net
drwxrwxr-x   3 lnxvm lnxvm   4096 Apr  8 09:11 mm
-rw-rw-r--   1 lnxvm lnxvm  60410 Apr  8 09:11 Makefile
-rw-rw-r--   1 lnxvm lnxvm 545614 Apr  8 09:11 MAINTAINERS
drwxrwxr-x   6 lnxvm lnxvm   4096 Apr  8 09:11 LICENSES
drwxrwxr-x  20 lnxvm lnxvm  12288 Apr  8 09:11 lib
drwxrwxr-x  18 lnxvm lnxvm   4096 Apr  8 09:11 kernel
-rw-rw-r--   1 lnxvm lnxvm    595 Apr  8 09:11 Kconfig
-rw-rw-r--   1 lnxvm lnxvm   1327 Apr  8 09:11 Kbuild
drwxrwxr-x   2 lnxvm lnxvm   4096 Apr  8 09:11 ipc
drwxrwxr-x   2 lnxvm lnxvm   4096 Apr  8 09:11 init
drwxrwxr-x  28 lnxvm lnxvm   4096 Apr  8 09:11 include
drwxrwxr-x  78 lnxvm lnxvm   4096 Apr  8 09:11 fs
drwxrwxr-x 138 lnxvm lnxvm   4096 Apr  8 09:11 drivers
drwxrwxr-x  81 lnxvm lnxvm   4096 Apr  8 09:11 Documentation
drwxrwxr-x   4 lnxvm lnxvm   4096 Apr  8 09:11 crypto
-rw-rw-r--   1 lnxvm lnxvm  99724 Apr  8 09:11 CREDITS
-rw-rw-r--   1 lnxvm lnxvm    496 Apr  8 09:11 COPYING
drwxrwxr-x   2 lnxvm lnxvm   4096 Apr  8 09:11 certs
drwxrwxr-x   3 lnxvm lnxvm   4096 Apr  8 09:11 block
drwxrwxr-x  27 lnxvm lnxvm   4096 Apr  8 09:11 arch
lnxvm@lnxvm-VirtualBox:/usr/src/kernel/linux-5.6.3$ make help
Cleaning targets:
  clean           - Remove most generated files but keep the config and
                    enough build support to build external modules
  mrproper        - Remove all generated files + config + various backup files
  distclean       - mrproper + remove editor backup and patch files

Configuration targets:
  config          - Update current config utilising a line-oriented program
  nconfig         - Update current config utilising a ncurses menu based program
  menuconfig      - Update current config utilising a menu based program
  xconfig         - Update current config utilising a Qt based front-end
  gconfig         - Update current config utilising a GTK+ based front-end
  oldconfig       - Update current config utilising a provided .config as base
  localmodconfig  - Update current config disabling modules not loaded
  localyesconfig  - Update current config converting local mods to core
  defconfig       - New config with default from ARCH supplied defconfig
  savedefconfig   - Save current config as ./defconfig (minimal config)
  allnoconfig     - New config where all options are answered with no
  allyesconfig    - New config where all options are accepted with yes
  allmodconfig    - New config selecting modules when possible
  alldefconfig    - New config with all symbols set to default
  randconfig      - New config with random answer to all options
  yes2modconfig   - Change answers from yes to mod if possible
  mod2yesconfig   - Change answers from mod to yes if possible
  listnewconfig   - List new options
  helpnewconfig   - List new options and help text
  olddefconfig    - Same as oldconfig but sets new symbols to their
                    default value without prompting
  kvmconfig       - Enable additional options for kvm guest kernel support
  xenconfig       - Enable additional options for xen dom0 and guest kernel
                    support
  tinyconfig      - Configure the tiniest possible kernel
  testconfig      - Run Kconfig unit tests (requires python3 and pytest)

Other generic targets:
  all             - Build all targets marked with [*]
* vmlinux         - Build the bare kernel
* modules         - Build all modules
  modules_install - Install all modules to INSTALL_MOD_PATH (default: /)
  dir/            - Build all files in dir and below
  dir/file.[ois]  - Build specified target only
  dir/file.ll     - Build the LLVM assembly file
                    (requires compiler support for LLVM assembly generation)
  dir/file.lst    - Build specified mixed source/assembly target only
                    (requires a recent binutils and recent build (System.map))
  dir/file.ko     - Build module including final link
  modules_prepare - Set up for building external modules
  tags/TAGS       - Generate tags file for editors
  cscope          - Generate cscope index
  gtags           - Generate GNU GLOBAL index
  kernelrelease   - Output the release version string (use with make -s)
  kernelversion   - Output the version stored in Makefile (use with make -s)
  image_name      - Output the image name (use with make -s)
  headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH
                    (default: ./usr)

Static analysers:
  checkstack      - Generate a list of stack hogs
  namespacecheck  - Name space analysis on compiled kernel
  versioncheck    - Sanity check on version.h usage
  includecheck    - Check for duplicate included header files
  export_report   - List the usages of all exported symbols
  headerdep       - Detect inclusion cycles in headers
  coccicheck      - Check with Coccinelle

Tools:
  nsdeps          - Generate missing symbol namespace dependencies

Kernel selftest:
  kselftest       - Build and run kernel selftest (run as root)
                    Build, install, and boot kernel before
                    running kselftest on it
  kselftest-clean - Remove all generated kselftest files
  kselftest-merge - Merge all the config dependencies of kselftest to existing
                    .config.

Userspace tools targets:
  use "make tools/help"
  or  "cd tools; make help"

Kernel packaging:
  rpm-pkg             - Build both source and binary RPM kernel packages
  binrpm-pkg          - Build only the binary kernel RPM package
  deb-pkg             - Build both source and binary deb kernel packages
  bindeb-pkg          - Build only the binary kernel deb package
  snap-pkg            - Build only the binary kernel snap package
                        (will connect to external hosts)
  dir-pkg             - Build the kernel as a plain directory structure
  tar-pkg             - Build the kernel as an uncompressed tarball
  targz-pkg           - Build the kernel as a gzip compressed tarball
  tarbz2-pkg          - Build the kernel as a bzip2 compressed tarball
  tarxz-pkg           - Build the kernel as a xz compressed tarball
  perf-tar-src-pkg    - Build perf-5.6.3.tar source tarball
  perf-targz-src-pkg  - Build perf-5.6.3.tar.gz source tarball
  perf-tarbz2-src-pkg - Build perf-5.6.3.tar.bz2 source tarball
  perf-tarxz-src-pkg  - Build perf-5.6.3.tar.xz source tarball

Documentation targets:
 Linux kernel internal documentation in different formats from ReST:
  htmldocs        - HTML
  latexdocs       - LaTeX
  pdfdocs         - PDF
  epubdocs        - EPUB
  xmldocs         - XML
  linkcheckdocs   - check for broken external links
                    (will connect to external hosts)
  refcheckdocs    - check for references to non-existing files under
                    Documentation
  cleandocs       - clean all generated files

  make SPHINXDIRS="s1 s2" [target] Generate only docs of folder s1, s2
  valid values for SPHINXDIRS are: hwmon vm openrisc sh leds virt mips arm64 powerpc driver-api accounting RCU target dev-tools timers power networking input cdrom infiniband sound media core-api w1 pcmcia netlabel riscv kbuild userspace-api watchdog s390 filesystems fb livepatch hid kernel-hacking arm translations scheduler m68k firmware-guide isdn x86 doc-guide block locking spi usb maintainer process sparc PCI bpf security xtensa misc-devices fault-injection mic parisc ia64 i2c gpu fpga admin-guide trace ide crypto iio

  make SPHINX_CONF={conf-file} [target] use *additional* sphinx-build
  configuration. This is e.g. useful to build with nit-picking config.

  Default location for the generated documents is Documentation/output

Architecture specific targets (x86):
* bzImage      - Compressed kernel image (arch/x86/boot/bzImage)
  install      - Install kernel using
                  (your) ~/bin/installkernel or
                  (distribution) /sbin/installkernel or
                  install to $(INSTALL_PATH) and run lilo
  fdimage      - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)
  fdimage144   - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)
  fdimage288   - Create 2.8MB boot floppy image (arch/x86/boot/fdimage)
  isoimage     - Create a boot CD-ROM image (arch/x86/boot/image.iso)
                  bzdisk/fdimage*/isoimage also accept:
                  FDARGS="..."  arguments for the booted kernel
                  FDINITRD=file initrd for the booted kernel

  i386_defconfig              - Build for i386
  x86_64_defconfig            - Build for x86_64

  make V=0|1 [targets] 0 => quiet build (default), 1 => verbose build
  make V=2   [targets] 2 => give reason for rebuild of target
  make O=dir [targets] Locate all output files in "dir", including .config
  make C=1   [targets] Check re-compiled c source with $CHECK
                       (sparse by default)
  make C=2   [targets] Force check of all c source with $CHECK
  make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections
  make W=n   [targets] Enable extra build checks, n=1,2,3 where
                1: warnings which may be relevant and do not occur too often
                2: warnings which occur quite often but may still be relevant
                3: more obscure warnings, can most likely be ignored
                Multiple levels can be combined with W=12 or W=123

Execute "make" or "make all" to build all targets marked with [*]
For further info see the ./README file
lnxvm@lnxvm-VirtualBox:/usr/src/kernel/linux-5.6.3$

lnxvm@lnxvm-VirtualBox:/usr/src/kernel/linux-5.6.3$ make menuconfig
  LEX     scripts/kconfig/lexer.lex.c
  YACC    scripts/kconfig/parser.tab.[ch]
/bin/sh: 1: bison: not found
scripts/Makefile.host:17: recipe for target 'scripts/kconfig/parser.tab.h' failed
make[1]: *** [scripts/kconfig/parser.tab.h] Error 127
Makefile:568: recipe for target 'menuconfig' failed
make: *** [menuconfig] Error 2
lnxvm@lnxvm-VirtualBox:/usr/src/kernel/linux-5.6.3$ make oldconfig
  YACC    scripts/kconfig/parser.tab.[ch]
/bin/sh: 1: bison: not found
scripts/Makefile.host:17: recipe for target 'scripts/kconfig/parser.tab.h' failed
make[1]: *** [scripts/kconfig/parser.tab.h] Error 127
Makefile:568: recipe for target 'oldconfig' failed
make: *** [oldconfig] Error 2

Before you re-test, do read {kernel source dir}/Documentation/process/changes.rst. It's a text file with a bit of mark-up (not much).

where is this  {kernel source dir}/Documentation/process/changes.rst.

In your Kernel Source Directory. The same directory where you type make. Instead of make, enter less Documentation/process/changes.rst